Mail

MIME Builder

MIME Message Creation

Enter your message and attachments to generate a complete raw MIME message.

Message details

Use sender@example.com or Alice <sender@example.com>. Separate recipients with commas. ASCII email addresses only; display names can use any supported Unicode text. Up to 50 recipients across To, Cc and Reply-To.

From

Cc (optional)

Reply-To (optional)

Subject

Date

Include a timezone offset, e.g. 2026-09-24T10:00:00+09:00. “Use current time” fills your local time and offset.

Message content

Enter plain text, HTML, or both. UTF-8, transfer encoding and multipart structure are automatic. Text uses CRLF line endings and a final newline. Attachments alone create an empty plain-text part.

Plain textHTML source

HTML source only; no rendering or remote images. Tab moves to the next field. Use Ctrl+] / Ctrl+[ to indent or outdent lines.

Attachments

Files stay in this browser. Up to 10 files; 768 KiB per file, 1 MiB combined. Generated MIME: 2 MiB maximum. File type comes from the browser, with application/octet-stream as fallback.

Add files

Processed locally. No input is uploaded or stored.

Each body: 65,536 characters. Subject: 300 characters. Filenames: 255 characters. No SMTP sending, signing or inline image generation.

MIME Builder

Message summary

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