web performance and seo
SMTP limit
The maximum total size of a single email message including all attachments enforced by mail servers.
What is SMTP limit?
An SMTP limit is the maximum total size of a single email message — including all attachments — enforced by a mail server using the Simple Mail Transfer Protocol. The most restrictive server in an email's delivery chain determines whether the message is delivered successfully. Common SMTP limits in 2026 include Gmail's 25 MB outbound limit, Outlook and Microsoft 365's 20 MB limit, and corporate Exchange servers typically configured at 10–15 MB.
Importance of SMTP limit
Understanding SMTP limits prevents email delivery failures and ensures your image attachments reach recipients reliably. Without proper email attachment size limit awareness, your compressed images may still bounce back from restrictive corporate servers or government systems. This is especially critical when sending multiple photos for social media campaigns or client reviews via email.
SMTP limit in Practice
When sending photos via Gmail, your total attachment size cannot exceed 25 MB, but files are base64-encoded during transmission, adding 33% overhead. A folder of wedding photos measuring 20 MB on your computer becomes approximately 26.6 MB after encoding, causing Gmail to reject the message. Corporate email servers often have stricter limits — a 15 MB photo collection may bounce from a client's Exchange server configured at 10 MB.
SMTP limit Best Practices
- → Compress images to keep total attachment data under 7–8 MB before base64 encoding overhead.
- → Test email delivery to corporate recipients before sending large batches of compressed photos.
- → Use Pictuary's combined compress and resize tool to reduce file sizes while maintaining quality for email distribution.
Example of SMTP limit
Related Terms
Frequently Asked Questions
What is SMTP limit for Gmail?
Gmail's SMTP limit is 25 MB for outbound emails including all attachments. However, files are base64-encoded during transmission, adding approximately 33% overhead to your actual file sizes. To ensure delivery through Gmail, keep your total attachment data under about 19 MB before encoding.
Why does my email attachment get rejected for being too large?
Your email attachment gets rejected because it exceeds the SMTP limit of the most restrictive server in the delivery chain. Even if Gmail allows 25 MB attachments, the recipient's corporate server might limit emails to 10 MB or less. Base64 encoding also increases file sizes by 33% during transmission, making attachments larger than they appear on your computer.
What is the maximum file size I can send through email reliably?
To reliably clear every server in an email delivery chain, keep total attachment data under 7–8 MB before encoding. This accounts for base64 encoding overhead and conservative corporate server limits. Files measuring 7 MB on disk become approximately 9.3 MB after encoding, staying well below most restrictive SMTP limits.