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Queued Email: The Reasons Behind Delayed Delivery

queued email cover image with a queue sign

A “queued email” is an email message that is scheduled for delivery but is waiting to be sent to mail servers. Instead of being sent immediately upon composition, these emails are placed in a queue within an email system or email marketing platform, either intentionally or due to technical problems.

It’s important to point out that queued emails can mean different things in different contexts. For example, queued emails mean different things for personal email users and email marketing professionals. Additionally, such emails need not always be a technical concern; in some scenarios, queued can even come in handy.

We’re going to unravel this mysterious function and help you fully understand its role in email communication.



What are Queued Emails?

Queued emails are messages that are waiting to be sent by the server. This could either be due to a temporary issue — like a poor internet connection or a technical problem — or because the email platform is intentionally queuing the emails to avoid sending them all at once.

So queued emails can be used intentionally or it may indicate a problem. As the term means different things in the context of personal email and email marketing, we’re going to list them all.

Queued emails as a feature:

  • In personal email use, messages that are composed and scheduled to be sent at a later time are called queued emails. This feature is commonly available in email clients/services, allowing users to draft emails and set a specific date and time to send them.
  • In email marketing, messages that are queued up for delivery as part of an email campaign are called queued emails. Marketers use email marketing platforms to schedule and automate the sending of emails to their subscribers.

Queued emails as a bug:

  • For regular email users, a queued email could mean the email they’re trying to send is stuck in the outbox. Common causes include large file attachments, connectivity issues, low device storage, or even account restrictions; we’ll expand on these reasons below.
  • In email marketing, when emails are stuck in an email service provider’s (ESP) queue, it’s referred to as queued emails. It could occur due to sending limits, invalid email addresses, technical issues with the ESP’s queue data set, or even an issue with the ESP’s mail servers. We will cover this in detail shortly!

As you can tell, it’s important to understand the phenomenon of queued emails so your emails are delivered correctly.


Queued Emails for Personal Email Users

First, let’s talk about why users of platforms like Gmail, Yahoo, or Outlook would want to use queued emails.

Regular email users find this feature useful for scheduling birthday greetings, reminders, or important announcements to be sent at a later time, ensuring messages are delivered when they are most relevant or convenient for the recipient.

Queued emails offer convenience; they allow users to compose messages whenever they have time and schedule them for delivery later. 

But let’s say a user didn’t want their emails queued and finds a bunch of them stuck in the outbox. What could be the reason then?

Why Do Emails Get Queued?

Common reasons for emails to get queued include:

  • Connectivity issues: A poor internet connection or problems with the email provider can cause emails to be queued.
  • Low storage space: If you’re low on storage space in your email account, your emails may be queued until there’s enough space.
  • Sending large files: If you’re sending large files via email, they may be queued until the data is uploaded, especially if you have connectivity issues.
  • Device storage: If your device is running out of space, it may have trouble uploading data, causing emails to be queued.
  • Inbox restrictions: If you’re sending a large number of emails, say, with a free Google account, Gmail may impose restrictions that cause your emails to be queued.
  • Blocked IP address: If your IP address has been blocked, you may need to unlist yourself and talk to your mailbox provider’s support team to avoid having your emails queued.
  • Technical issues: There could be other technical issues with the email server or recipient’s server that cause emails to be queued

In most cases, these stuck emails will be delivered later once the issue has been resolved. 


Troubleshoot Queued Emails in Gmail, Yahoo, Outlook, and Apple Mail

Queued Email on Apple Mail
Example of a queued email in the Apple Mail outbox

Gmail, Apple, Yahoo, and Outlook are among the most popular mailbox providers — this section will walk you through troubleshooting stuck emails on these platforms.

These 6 steps should clear up your queue:

  1. Ensure you have a stable internet connection, as poor connectivity can cause emails to be queued.
  2. If there are server problems, either with your mailbox provider or your recipient’s, it can cause queued emails. Contact your mailbox provider for assistance or ask the recipient to contact theirs.
  3. If you’re using a mobile device, ensure that it’s not running low on storage or experiencing any other issues that could be causing the queuing of emails.
  4. Clearing the app cache can help resolve issues with emails stuck in a queue. You can find this option in the settings or preferences of the email client/service.
  5. Look for the “Outbox” folder to see if any emails are stuck there. If you find emails in the outbox, try resending them by opening the email and clicking “Send.”
  6. If you’re using your mailbox provider’s app, make sure you are on the latest version, as updates often include bug fixes that can address queuing problems.

An additional step for Gmail users on Android phones is Gmail’s “Sync” option. Sometimes, queueing issues occur because of an error in Gmail’s syncing abilities. You can try disabling and re-enabling Gmail sync in your device’s Settings app to see if it resolves the issue.

That wraps up queued emails for personal email users; let’s see what role they play in marketing emails.


Queued Emails in Email Marketing

Queuing emails is a common practice in email marketing. It helps manage the sending of bulk emails in a way that ensures high deliverability and avoids triggering spam filters. 

When you send a large number of emails, the SMTP server on your host puts them in a queue to allow for periodic sending until completion. This can help prevent overloading the recipient’s server or activating spam filters that might be triggered by a large number of emails coming from the same IP address in a short period of time.

Managing an email queue is an important task for email marketers; it can help ensure your emails are delivered in a timely and efficient manner. This can involve monitoring the queue for any issues or errors, optimizing the email campaign to avoid being flagged as spam, and working with your mail provider to resolve any issues.


Advantages of Queued Emails

Curious about why email marketers would use queued emails?

Email marketers get these advantages from queued emails:

Benefits of queueing emailsHow it helps email marketers
Efficient campaign managementHelps plan and schedule email campaigns in advance
Time zone optimizationReach recipients in different time zones at the most appropriate times
Consistency in communicationSet up a regular cadence for emails, ensuring the audience receives timely, relevant content
Better engagement ratesBy scheduling emails to send during peak engagement hours, marketers can improve results
Reduced workloadAutomating the process of sending messages reduces manual effort
A/B testingOpportunity to conduct A/B testing
Queued Emails: Benefits in Email Marketing

Overall, queued emails offer marketers greater control and flexibility in managing their email marketing campaigns, which results in an engaged and enthusiastic audience.


Troubleshooting: Queued Emails Stuck in Outbox

Are you on your email platform, desperately trying to figure out why your emails are queued up in the outbox and not sending? You’d be surprised at the number (and variety!) of reasons that can cause this problem. 

Why are Emails Stuck in My ESP Outbox?

If you see emails stuck in a queue on your email platform, it could be due to any of these causes:

ReasonWhat does it mean?
Invalid list Contains inaccurate, outdated, or unengaged email addresses.
Sending volumeSending a massive email campaign at once can overwhelm the ESP’s servers.
Scheduled sendingEmails are intentionally placed in the queue to be delivered at a specific future time.
Technical issuesTemporary glitches with the ESP’s servers can disrupt email delivery.
Large attachments or file issuesEmails with large attachments or corrupt/invalid files can cause the email to get stuck in the outbox.
Connectivity issuesUnstable internet connection on your end
Other appsConflicting apps can cause the email to get stuck in the outbox.
ESP limitsSome ESPs have limitations on the number of emails you can send within a specific timeframe.
API codingIf you’re accessing your ESP API directly, incorrect coding can cause queued emails.
Insufficient CRM dataIf your ESP gets incorrect or insufficient data from your CRM, it can cause email sending to fail and accumulate in your outbox.
Domain warmupIf you have not warmed up your domain sufficiently, as per ESP guidelines, they can freeze sending.
Queued emails on email marketing platform: Causes

How to Fix Queued Emails

To troubleshoot stuck emails in the ESP outbox, you can try these 13 steps:

  1. Verify configuration details: Start with checking incorrect recipient addresses, mail server blacklisting, or email domain configuration problems.
  2. Check for connectivity issues: Ensure the ESP isn’t struggling with connectivity issues. Check the platform’s status page for any reported issues.
  3. Check send date and time: Check if you scheduled the campaign for a future date — emails wait in the queue until the scheduled time arrives.
  4. Check server settings: Check the settings of your SMTP server to ensure they are correctly configured.
  5. Check DNS data: Ensure your domain’s DNS settings are properly configured, including SPF, DKIM, and DMARC records.
  6. Try later: Avoid sending large campaigns during peak usage times.
  7. Examine email content: Review the content of the emails stuck in the queue; it’s possible your ESP stalled the sending process because they detected issues with the email content.
  8. Address sender reputation problems: If your sender reputation is low, the ESP can freeze your account. Work on your sender score until it improves.
  9. Use batch sending: Organize your outgoing emails based on importance to minimize queuing.
  10. Check file sizes: Avoid sending emails with large attachments, as they can cause delays and lead to emails being queued.
  11. Check logs and reports: Monitor email logs and delivery reports provided by your ESP.
  12. Email list hygiene is critical: Regularly clean your email list to remove inactive subscribers and improve overall deliverability.
  13. ESP limits: If you’re sending a massive campaign, the platform might be batching them to avoid overwhelming servers. Check the platform’s documentation for typical sending speeds.

If you’ve exhausted all troubleshooting steps and the queue persists, reach out to the ESP’s support team.


Email List Cleaning: Critical for Smooth Email Delivery

When an email is stuck in the outbox, it could be due to various reasons — connectivity issues, server issues, or issues with the recipient’s email server. One of the most common causes, however, is that your email list contains invalid email addresses; this can create an email queue in your outbox.

Email list cleaning is simply the process of ensuring your email list is up-to-date and only contains valid email addresses.

When you send an email to an invalid address, it can result in a bounce-back or a soft bounce. If this happens frequently, it can affect your sender reputation and cause your emails to be flagged as spam. This can lead to your ESP flagging your account and holding your emails in the outbox until the issue is resolved.

Even if you manage to send the stuck emails, a dirty contacts list means your sender reputation takes a bad hit, and your deliverability rates tank — an undesirable situation.

List cleaning can help prevent this by removing inactive email addresses from your email list. 

This is why Campaign Refinery features an automated list-cleaning tool; it analyzes your list and removes all kinds of problematic entries such as spam traps, seeder accounts, temporary emails, role-based emails, bots, and complainers. 

The result? Mailbox providers don’t raise red flags when our emails reach their servers!

Email List Cleaning: Best Practices

Want to avoid queued emails due to poor list quality?

These list management tips will help avoid delivery and deliverability issues.

  • Clean your list at least quarterly, or even more frequently depending on list size and acquisition methods.
  • Address both types of bounces — hard bounces (permanent failures) and soft bounces (temporary issues).
  • Segment your list based on demographics, interests, or engagement levels for more targeted and relevant email campaigns.
  • Remove subscribers who haven’t opened or clicked on your emails in a set timeframe (typically 3-6 months)
  • Implement a double opt-in process where subscribers confirm their email addresses to reduce typos and invalid addresses.
  • Use email verification tools to check the validity of email addresses on your list.
  • Avoid role-based addresses as they are less likely to be engaged.
  • Allow subscribers to manage their preferences and update their contact information.
  • Make it easy for subscribers to unsubscribe from your emails with a prominent and user-friendly unsubscribe link in every email. This helps reduce spam complaints.

As you focus on list hygiene and prioritize it, you will see your email performance improve with time!


Queued Emails at Campaign Refinery: Lightning-Fast

As the number one deliverability email platform, we know everything there is to know about efficient and accurate email delivery. When we say our emails go out fast, we mean it — our email-sending speeds are among the fastest in the industry right now.

Even with massive lists, Campaign Refinery sends emails at a fraction of the time it takes our competitors.

In fact, we’re so fast that we had to dial it back a bit to keep mailbox providers happy. As excessive sends can negatively impact deliverability, we fine-tuned our sending engine to hit the sweet spot in terms of speed and efficiency with zero compromises on inbox placements. 

This table explains the key Campaign Refinery features focused on efficiency:

AspectExplanationEffect
Authentication protocols mandateWe require all clients to implement authentication protocolsMailbox providers see our clients’ emails as trustworthy
New customer screeningA vetting process to approve new clients before they can send emailsEnsures we don’t onboard any spammers that can wreck our reputation
Traffic monitoringWe constantly monitor servers to ensure optimal performanceConsistent low engagement or complaints can lead to account suspension
Automated list-cleaning toolThis feature validates the emails in your contacts listBy removing invalid emails, the tool protects your sender score
Tagging and segmentation toolsSmartly organize your email contacts Makes it convenient to clean and organize lists for better engagement and targeting
Campaign Refinery: Experts on Email Delivery

At Campaign Refinery, elite email performance is all we do. Apply to be a customer today!

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