- Large attachments. Remember that email encoding makes attachments about a third larger than the original files.
552 5.3.4: Message too large
AnySMTP
The error usually looks like this:
What it means
The message, including attachments, is larger than the server allows.
Common causes
How to fix it
- Send smaller attachments, or share large files using a link instead.
Tools to help diagnose it
A free tool provided by Auth-Email
Auth-Email makes your Gmail, Outlook, or other OAuth 2.0 email account available to any IMAP, POP3, or SMTP email client — no app passwords or special configuration needed.