Unsupported Attachment Types

Documents: .pdf , .docx , .xlsx , .pptx , .csv , .txt
Images: .png , .jpg , .jpeg , .gif , .webp , .svg
Archives: Standard .zip and .tar.gz (containing safe documents)
Calendar: .ics

To prevent malware propagation and ensure high inbox delivery rates, Mailofly restricts certain executable, script, and high-risk attachment types.

Blocked File Extensions

The following file extensions are strictly blocked by Mailofly and major receiving mail transfer agents (Gmail, Outlook, Yahoo):

Category	Blocked Extensions
Executables	`.exe`, `.dll`, `.bin`, `.msi`, `.dmg`, `.iso`, `.com`
Scripts & Code	`.bat`, `.cmd`, `.sh`, `.vbs`, `.js`, `.jse`, `.ps1`, `.scr`
System Archives	Password-protected or encrypted archives containing executables

If an email payload includes a blocked file type, the API rejects the request with an HTTP 400 error.

Maximum Total Payload: 25 MB per email (including headers, HTML content, and base64-encoded attachments).
Base64 Overhead: Base64 encoding inflates binary file size by approximately 33%. For example, a raw 18 MB file will encode to ~24 MB.
Large Files: For attachments exceeding 20 MB, we recommend hosting the file (e.g. AWS S3, Cloudflare R2, Google Cloud Storage) and providing a secure download link in the email body.