We have a 500MB limit on the size of emails forwarded by our system, which means the allowable size of attachments is lower once you account for email protocol overheads.
However, the end mail account can have (and in most cases they do have) limits regarding size and attachments.
- Gmail size limit: 25MB
- Outlook size limit: 20MB
- Hotmail size limit: 10MB
- Office 365 size limit: 150MB
- Yahoo size limit: 25MB