Usually suitable for standard forwarding
Common documents, images, and small archives are more likely to pass each stage’s limits. Still verify the attachment source and scan it with security software.
Rules by size · Email attachment limits
How large can an attachment be and still be forwarded and retained?
Attachment size is more than the file size shown on your drive. Email encoding adds overhead, and the sending server, our service, and the destination mailbox may each have their own limits.
Start with four size ranges
Use these ranges for planning and troubleshooting—not to bypass any provider’s limits. Actual results also depend on the full message, number of files, encoding, and destination mailbox policies.
Enter the compatibility watch zone
Some mailboxes may reject the message or convert the attachment into a cloud link. Multiple files and HTML content can make the full message larger than the attachments alone.
Not suitable for relying on direct forwarding
Encoding can make the message significantly larger than the original files, and any upstream or destination mailbox may reject it. Prefer a link from a trusted file-sharing service.
Use a dedicated transfer channel
Don’t repeatedly retry very large attachments. Use a file-transfer service with access controls, expiration, and verification, then email the link.
Why a 40 MB file can become a much larger email
Binary attachments typically pass through encoding such as Base64 and include MIME boundaries, filenames, and message content. Leave room for encoding overhead when estimating size.
| Total original attachment size | Approximate encoded size | Risk level | Recommendation |
|---|---|---|---|
| 5 MB | About 6.7 MB plus message content | Low | Send normally, but still verify the source |
| 20 MB | About 26.7 MB plus message content | Medium | Check both mailbox limits |
| 40 MB | About 53.3 MB plus message content | High | Prefer using a sharing link |
| 75 MB | About 100 MB plus message content | Very high | Use a dedicated transfer service |
Which checkpoints does an attachment email pass through?
When you see a “failed” status, first identify where the rejection occurred. Blindly clicking retry only repeats the same limitation.
Sending server
The sender’s server may reject the attachment during upload or trim it according to its own limits.
Receiving and security checks
File type, malicious content, total size, and archive policies can all affect acceptance.
Forwarding process
The system reads the original message and delivers it to the real mailbox while recording whether it succeeded, failed, or was marked as spam.
Destination mailbox
The final provider may reject delivery because of quotas, attachment limits, or security policies.
What to do after a failure
A failed status in the archive is a troubleshooting clue, not a guarantee that the file is stored permanently and safely. After the 30-day window ends, the record enters cleanup.
Check the status and time first
Confirm that the failure occurred with this message and check whether the destination mailbox was full or temporarily unavailable at the time.
Confirm the file type
Executables, encrypted archives, and macro-enabled documents are more likely to be blocked by security policies. Don’t disguise a file extension to get around a limit.
Retry small files cautiously
If the cause was a temporary network or destination-mailbox issue, you can retry once after it is resolved. If failures continue, stop clicking and use another channel.
Send large files as controlled-access links
Set access permissions, an expiration date, and download limits before sending the link to the recipient. Sensitive material should also use organization-approved encryption.
Why attachment limits can’t be reduced to one number
Email is a chain of multiple stages, and the tightest limit determines the final result. Even if our service accepts the message, the destination mailbox may reject it because of total message size, quotas, or file policies.
That’s why 50 MB and 100 MB are better treated as risk bands than guaranteed delivery thresholds. The closer you get to a limit, the more you should use dedicated file transfer instead of repeatedly trying to send the message.
Are temporary inboxes suitable for attachments?
Small, low-sensitivity attachments that only need to be read once can be handled during the active period, but a temporary inbox is not a backup service. Once the address expires, you should not expect to recover the files.
Attachments from unknown sources can be dangerous even when they download successfully. Don’t run programs, macros, or unfamiliar archives directly on an important device.
How long are forwarded messages retained?
The dashboard provides delivery records and details for up to 30 days, so you can check successful, failed, and spam statuses. It does not replace long-term storage in a real mailbox or serve as a document management system.
For legitimate files that need long-term retention, verify their source and move them to storage you control with backups, while following your organization’s data-handling policies.