Email Attachment Size Limit: A Comprehensive Guide
Email attachment size limit continues to be a critical factor in email delivery. Most email service providers (ESPs) impose strict size restrictions, typically ranging from 10MB to 25MB per email.
However, just because you can send larger attachments doesn’t mean you should. Understanding these limitations isn’t just about avoiding bounced emails.
It’s about:
- Optimizing email deliverability rates,
- Maintaining your email sender reputation,
- Ensuring your marketing messages actually reach their intended audience.
Let’s explore why size matters in email marketing and how to work within these constraints effectively.
What is the Email Attachment Size Limit?
The email attachment size limit is the maximum file size that can be attached to an email and sent to recipients without being rejected or blocked by the email provider. This restriction is imposed to manage email server load and protect against potential security risks such as malware.
Email size limits apply to both individual file attachments and the combined total of all elements of an email. This includes text, formatting, and metadata like email headers and MIME encoding. These elements can inflate the actual size of an email beyond just the raw attachment data.
The email file size limit impacts various aspects of email functionality:
- File transfer speeds: Large files require more network resources to transfer, which can slow down email delivery and consume a significant amount of bandwidth.
- Server storage: Each mailbox provider’s server has finite storage space; limiting attachment sizes ensures emails can be stored efficiently.
- Optimal processing: File limits ensure the smooth server processing of emails without compromising performance.
- Data security: Controlling attachment sizes helps reduce exposure to large files that could contain security threats, such as viruses or malicious software, which are often embedded in large files.
Email Attachment Size Limits of Popular Email Services
It’s not uncommon to see error messages when attaching large files to emails. This happens because all mailbox providers impose a limit on email attachment size. In most cases, it also applies to incoming emails.
| Email Client or Service | File Attachment Size Limit |
|---|---|
| Gmail | 25 MB |
| Google Workspace | 25 MB |
| Outlook (Web) | 20 MB |
| Yahoo Mail | 15 MB |
| iCloud Mail | 20 MB |
| Microsoft 365 (Outlook) | ‣ 150 MB (Desktop) ‣ 112 MB (Web) ‣ 33 MB (Mobile) |
| ProtonMail | 25 MB |
| Zoho Mail | 10 MB |
It’s not just mailbox providers that restrict large attachments. Email platforms, too, are not keen on customers including large email attachments in marketing. We explain why in the next section.
Size Limits in Email Marketing
When you send thousands of emails at once to multiple recipients, email size becomes crucial. A low size ensures these campaigns reach inboxes without encountering issues that can impact deliverability or user engagement. This is why between HTML vs plain text emails, the latter is capable of superior inbox placement.
Most ESPs don’t even allow email attachments as it directly affects email deliverability.
Let’s check out the 7 reasons why email size limits are essential and why email attachments are discouraged in email marketing.
1. Efficient Email Delivery
ESPs and Internet Service Providers (ISPs) have limited server resources to manage the high volume of email traffic that flows through their systems daily. When a campaign is excessively large, it is an additional strain on the servers that process and deliver these emails.
2. Mail Server Load Management
By enforcing a size limit, ESPs ensure each email can be delivered swiftly without risking delays or failures due to high server load. This limit is especially relevant for those who send mass emails, as small attachments or links are much more manageable and have a lower risk of causing queued emails.
3. Spam Filters
Many ISPs and ESPs use sophisticated spam filtering algorithms to detect and block emails that resemble spam or potential phishing email attacks. Emails with attachments are more likely to trigger these spam filters.
4. User Experience
A smooth user experience is central to effective email marketing.
Large emails not only slow down opening speed but can also frustrate users with issues such as:
- Limited bandwidth,
- Mobile data plans,
- Older, slower devices.
These factors can lead to lower email engagement and more email bounces. For instance, a subscriber might abandon an email if it takes too long to load.
5. Data Security
Attachments often pose security risks, as they are more likely to contain malware or viruses, making ESPs cautious. By banning attachments, ESPs help protect email recipients from potential threats.
Using links to secure content ensures recipients trust the content they receive. This practice builds credibility and reduces the risk of being marked as spam or blocked. Plus, it’s a good way to track email response rates.
6. Mobile Optimization
Mobile email marketing is big right now; with a growing number of email users accessing their inboxes via mobile devices, email marketers need to consider mobile compatibility.
Attachments are not only cumbersome but can also consume significant amounts of data, especially for mobile users on limited data plans.
7. Superior Analytics Data
Monitoring email campaign metrics is key to effective email marketing. When emails have attachments that cause delivery failure, metrics can become skewed. Slow loading can even affect recipient behavior, which then reflects in poor metrics.
Using URLs to link to downloadable resources allows email marketers to capture more accurate performance analytics, such as:
Alternatives to Email Attachments
Instead of attaching large files, which can increase bounces, trigger spam filters, and reduce engagement, email marketers can utilize a variety of alternatives to deliver content effectively.
The top 7 methods are listed below.
1. Links to Cloud Storage Services
Cloud storage services like Google Drive, Dropbox, or OneDrive, offer secure, accessible ways to share large files without needing direct email attachments.
Additionally, cloud services offer robust access controls, allowing users to manage who can view, edit, or download the content, which is essential for data security and brand trust.
| Pros | Cons |
|---|---|
| Cloud links bypass attachment size limits, improving deliverability | They require subscribers to leave the email client to access content |
| They offer secure access controls | Some users may have privacy concerns with third-party cloud links |
| They allow for easy updates to shared content without needing new links | Cloud links may require login or account creation |
| Trackable links provide insights into user engagement | Links may not be compatible with strict corporate firewalls |
2. Dedicated Landing Pages for Downloads
A highly effective approach in email marketing is to drive email marketing subscribers to a dedicated landing page. Instead of sending attachments, marketers can embed links to a visually engaging page. This strategy not only keeps emails light but also allows the tracking of user behavior.
| Pros | Cons |
|---|---|
| This method boosts engagement by driving traffic to custom pages | This method may require additional setup for each landing page |
| Landing pages support advanced tracking, providing insights into user behavior | Users may abandon the journey if pages are slow or difficult to navigate |
| There are no file size concerns | It may increase unsubscribe rates if subscribers prefer in-email content |
| It’s an opportunity for brand alignment through custom designs | External links may trigger spam filters if overused |
3. Inline Images and Embedded Content
Using embedded images, GIFs, or video thumbnails can entice subscribers to click through to hosted content.
Instead of attaching a large file, a small preview of the content, such as a report cover page, can be embedded along with an email CTA (call-to-action). This can link out to the full content hosted externally.
| Pros | Cons |
|---|---|
| Inline content makes emails visually engaging | File sizes for GIFs and high-quality images may still be large |
| This method is simple to implement | It requires linking to hosted content, potentially losing subscribers who avoid links |
| Most ESPs and devices support it | Too many visuals may reduce email readability and distract from CTA |
4. Personalized Download Links
For gated content like reports, case studies, or guides, email marketers can use personalized download links that lead subscribers to a specific download page after filling out a short form or verifying their email.
This method works well in email nurture campaigns, as it helps capture additional information about the subscriber. Many ESPs allow for automatic unique link generation, providing a personalized touch and tracking who downloads the content.
| Pros | Cons |
|---|---|
| This personalized user experience enhances engagement | It requires link generation for each user, which may add complexity |
| It helps capture additional lead information before downloading | Subscribers may perceive gated content as cumbersome |
| Links are easily trackable, showing exactly who downloads content | Redirecting users outside of email may lower overall click-through rates |
5. Embedded Forms and Surveys
If the content requires gathering input, such as feedback forms, email surveys, or event RSVPs, embedding forms directly into the email can streamline the user experience. Many email marketing tools allow the insertion of interactive forms that work without requiring a separate attachment.
| Pros | Cons |
|---|---|
| Embedded content streamlines user experience | Forms may not display correctly on all email clients |
| It eliminates the need for external links or attachments | This method may have limited functionality compared to external survey tools |
| It allows real-time data collection and tracking within email | Some ESPs restrict forms due to spam concerns |
| Embedded forms and surveys keep users in the email, reducing bounce rates | Limited design options may restrict brand customization |
6. QR Codes
Including QR codes in emails is a unique way to provide instant access to content without attachments. A QR code can link subscribers to a downloadable asset, website, or media file, especially useful for mobile users.
| Pros | Cons |
|---|---|
| QR codes offer easy access for mobile users | They’re less useful for desktop users |
| They add a visually engaging, interactive element | Not all recipients may be familiar with or comfortable using QR codes |
| They’re quick to set up | QR codes require adequate space within the email design for readability |
| They help keep the email light while directing users to large content files | QR code links may not be clickable for users without a scanning device |
7. Social Media Links
Directing subscribers to social media channels where rich media content is available can be an effective option. For example, linking to a LinkedIn document post, an Instagram video, or a Twitter thread provides a more dynamic experience than a static attachment.
| Pros | Cons |
|---|---|
| This method encourages engagement on social platforms, extending brand reach | Social links require followers to be active on social media |
| This method supports multimedia formats with rich engagement options (likes, shares) | Not all users may be comfortable linking their social media to email content |
| It can offer an effective way to grow a social following | Redirecting to social media may result in decreased email engagement |
| It allows tracking and interaction through platform analytics | Inconsistent experience across platforms may not be ideal for all content types |
Manage Email Size for Better Email Deliverability
Email size directly impacts deliverability in 4 key ways:
- Large emails are more likely to trigger spam filters; many spam filters automatically flag emails over 100-150KB. This higher scrutiny can reduce inbox placement rates.
- ISPs process smaller emails more efficiently. Some ISPs may delay or deprioritize larger emails in their queues.
- Smaller emails typically have higher email delivery rates.
- Large emails have higher bounce rates due to recipient server limits. Some email servers reject emails over certain size thresholds.
Curious to know what else you can do to improve email deliverability? Check out the next section.
Additional Tips to Help Improve Your Inbox Placement
Achieving the best email deliverability for different types of email campaigns is a continuous challenge for email marketers. It’s vital to pay attention to various aspects.
Below, we share 9 topics of interest that can help you improve your email game.
Campaign Refinery: Assured Top-Tier Email Performance
At Campaign Refinery, we offer robust email infrastructure and enforce a strict Acceptable Use Policy to ensure all customers can enjoy the best inbox placement in the industry.
We fine-tuned our sending engine to find the optimal sending speed so you don’t face issues such as deferred emails or poor delivery rates. To protect our sender reputation, we also screen customers before we onboard them, plus we have a mandate on email authentication protocols such as SPF, DKIM, and DMARC.
We continue to monitor our servers to ensure no spammy activities take place — this ensures mailbox providers continue to welcome your email campaigns.
Unlock the full potential of email marketing with Campaign Refinery — check out our signup page here.
