What is the limit of SMTP?

Simple Mail Transfer Protocol (SMTP) is the standard protocol for sending email over the internet. When you compose an email in your email client or webmail and hit send, SMTP is what transfers that email to the recipient’s email server.

A key question when using SMTP is: what are the size limits for emails? Like any data transfer protocol, SMTP enforces size restrictions to ensure emails can be delivered efficiently and reliably. Exceeding limits may cause emails to bounce back or fail to send.

What is the limit of SMTP?

In this article, we’ll cover common SMTP message size limits across major email providers, troubleshoot what happens when you exceed limits, and suggest strategies for sending large attachments.

Most Common SMTP Size Limits

Here are typical SMTP maximum message sizes across popular email platforms:

  • Gmail – 25MB for incoming email, 50MB for outbound with paid G Suite account
  • Outlook/Office365 – 150MB with Office 365, 10MB for free Outlook.com
  • Yahoo Mail – 25MB
  • iCloud Mail – 20MB
  • Zoho Mail – 25MB
  • Fastmail – 35MB
  • Mailchimp – 10MB per email
  • SendGrid – 10MB per email

So the most common SMTP limit is between 10-50MB for most providers. This restriction applies to the total message size including encoded attachments.

Some enterprises using Exchange Server or Google Workspace may have custom limits up to 150MB for outbound email. But inbound mailboxes usually have lower limits around 25-50MB.

What Happens When You Exceed SMTP Size Limits?

Exceeding the maximum SMTP message size will lead to delivery failures like bounced emails or unsent messages. Here are some common issues:

  • Bounced emails – The recipient’s mail server immediately rejects and bounces back emails over the size limit. You’ll see error notifications like “552 Message size exceeds fixed limit”.
  • Failed to send – Webmail providers may hold large emails in Outbox queues rather than immediately bouncing them. The message will display as “sending” but eventually fail with errors.
  • Truncated messages – Some mail servers may receive large emails but truncate them by removing attachments first. So the body text sends but attachments are stripped.
  • Blocked as spam – Oversized emails also look suspicious to spam filters. Even if they go through, spam filters may automatically flag or block them.
  • Email delivery delays – Larger messages take longer to send between servers. Recipients may receive emails much later than expected.

To avoid these issues, it’s best to proactively check and conform to size limits when sending emails with large attachments.

Size Limits for SMTP Extensions

In enterprise environments, SMTP can be extended with additional protocols that support larger message sizes:

  • Exchange Web Services (EWS) – Part of Exchange Server, EWS has a maximum message size of 150MB. Requires an Exchange account.
  • IMAP – Most IMAP servers have size limits matching the base SMTP protocol. But some may allow up to 150MB attachments.
  • Hybrid Mail – Services like SendGrid, Mailgun, Mailjet support message sizes up to 50MB by relaying through private SMTP servers.

So if your organization has Exchange or dedicated email infrastructure, the size limits may be higher than standard SMTP. But recipients at outside domains will still be subject to lower SMTP caps.

Strategies for Sending Large Emails Up to 25MB

If you need to email files larger than 25MB, there are a couple options:

  • Compress attachments – Zip or Rar archives take up much less space than original files. You can compress multiple files together.
  • Split into multiple emails – Send attachments in separate emails under the size cap that reference the same subject.
  • Use file sending services – Google Drive, Dropbox, WeTransfer allow sharing large files by email upload link instead of attaching directly.
  • Upload to cloud storage – Similarly, upload large files to Google Drive, Dropbox, OneDrive and share a download link via email.
  • Use email services API – Mailgun, SendGrid, Mailjet, Amazon SES allow programmatically sending large files through their SMTP servers.
  • Upgrade email provider – Paid G Suite and Office 365 accounts often have higher limits up to 150MB.

With some creativity, you can reliably send large files through email without bumping into annoying SMTP size restrictions.

Key Takeaways

  • Typical SMTP size limits for most email providers range between 10-50MB.
  • Exceeding size caps leads to bounces, failed delivery, truncated messages or delayed emails.
  • Compressing, splitting, uploading to cloud storage or using file sending services lets you reliably share large attachments.
  • Paid business email plans from G Suite and Office 365 offer higher size limits up to 150MB.


SMTP message size limits exist to ensure reliable email delivery without overloading mail servers. While you can’t control the caps set by major email platforms, there are various workarounds like compression and file sharing services that still let you send large attachments. Understanding and optimizing for default SMTP limits ensures your important emails will reach inboxes without pesky errors or delays.

Frequently Asked Questions

  1. What is the size limit for Gmail?
    Gmail has a 25MB limit for incoming email and 50MB for outgoing messages on paid G Suite accounts. Free Gmail is capped at 25MB.
  2. What is the SMTP size limit for Outlook?
    Outlook.com has a 10MB limit. Office 365 allows up to 150MB.
  3. What happens if you exceed SMTP size limits?
    Exceeding SMTP limits usually results in bounced emails or failed delivery with errors like “message size exceeds fixed limit”.
  4. Can you send a 50MB email?
    It’s not recommended to attach 50MB files directly. Better options are compressing attachments, splitting into multiple emails, or uploading to cloud storage and sharing the download link.
  5. What is the size limit for email attachments?
    Most ISP email services limit attachments to 25MB or less. G Suite, Office 365, and some enterprise systems allow up to 150MB attachments.
  6. What is the maximum size for an email?
    Default SMTP limits range between 10-50MB for most providers. With extensions like EWS or IMAP, some enterprises support up to 150MB emailed messages.
  7. Can an email be 100 MB?
    Most standard email providers don’t support sending 100MB emails over SMTP. Even with extensions, the practical limit is around 150MB. Above that, it’s better to use file sharing services.
  8. What is the maximum size for Gmail attachments?
    Gmail has a 25MB limit on attachments for free accounts. G Suite allows up to 50MB attachments.
  9. What is the size limit for emails?
    Common SMTP email size limits range between 10-50MB for most providers like Gmail, Yahoo, Outlook, iCloud. Enterprise systems may go up to 150MB.
  10. Can I send a 10GB email?
    No, a 10GB email is not feasible over standard SMTP protocols which max out around 25-50MB typically. alternatives like file sharing services would be required for such large files.
  11. What is the maximum size for Outlook emails?
    Outlook.com has a 10MB limit. Office 365 allows up to 150MB email sizes.
  12. What is the maximum attachment size for Yahoo mail?
    Yahoo Mail has a 25MB limit for attachments sent and received.
  13. What happens if an email is too big?
    Oversized emails may get bounced back immediately, fail to send, send without attachments, get flagged as spam, or delayed significantly.
  14. How do I compress large files to email?
    Use Zip or Rar compression tools to archive and compress large files into smaller packages that meet email size limits. This allows sending bigger attachments.
  15. What is the maximum size of email I can send?
    It depends on your email provider. Common limits:
    Gmail: 25MB (free), 50MB (G Suite)
    Outlook: 10MB (Outlook), 150MB (Office 365)
    Yahoo: 25MB
    iCloud: 20MB


In summary, typical SMTP email size limits range between 10-50MB for most major providers. Exceeding these limits can cause bounces, failed delivery or delayed emails. To send large attachments, compress files, split into multiple emails, use file sending services, or share cloud download links instead of attaching directly. Understanding default SMTP restrictions lets you successfully share bigger files through email without errors.

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