EMAIL DIAGNOSTICS

Email Payload & Attachment Cost Inspector

Inspect a saved .eml message locally. Measure MIME and base64 attachment bytes, estimate data transfer costs and export a report without message contents.

Open an .eml file or paste message source → Inspect MIME bytes → Export measurements

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Method, assumptions and source prices

Measure what your mail library builds An attachment grows when encoded for MIME. A three-byte payload becomes four base64 characters before line wrapping and message headers. This inspector measures the serialized source you provide and reports base64 data separately from the complete message. Use the result correctly The normalized wire count treats line endings as CRLF and text as UTF-8. SES publishes 10 MB for its v1 API and 40 MB for v2/SMTP, after encoding. This 2 MB local inspector cannot test those boundaries or guarantee server acceptance. Use the provider quota page for the applicable limit. The data-charge scenario multiplies measured base64 payload bytes by your monthly recipient copies at $0.12 per decimal GB. Inline images are included; non-base64 attachments are flagged rather than guessed. Sending fees, other transfers and taxes are excluded. Downloaded reports contain measurements, not message text or addresses.

Price snapshot: 2026-09-23. Verify current provider terms before buying. Prices and time inputs are estimates; no delivery or savings guarantee.

Sources: SES quotas · MIME transfer encoding · SES pricing

How to read your result

Base64 expands binary data to roughly four bytes for every three input bytes, before line breaks and MIME headers. Provider message limits apply to encoded messages. This diagnostic does not send email or test spam placement.

Twelve Tools directory

TheDevToolsDir

Reproduce a known result

The attachment decodes to ABC: three bytes represented by four base64 characters. Whole-message bytes also include MIME headers, boundaries and line endings.

Load Three-byte synthetic MIME attachment · Download synthetic example

Examples and troubleshooting

The size of a file on disk is only one part of an email message. MIME headers, boundaries, transfer encoding and line breaks also consume bytes. Inspect a representative message before extrapolating a monthly data estimate.

Estimate MIME attachment size and base64 overhead

Common questions

Why is my attachment bigger after encoding?

Base64 expands groups of three bytes into four characters and may add padding. MIME framing and line wrapping add more bytes.

Will this send the email or upload the .eml file?

No. File reading and parsing occur in the browser workspace. The tool has no send-email operation.

Can I share the report without exposing recipients?

The report deliberately omits raw content and identifying headers. Review the resulting file before sharing; do not share your original message by mistake.

Privacy and anonymous measurement

Your tool inputs stay in the isolated browser workspace. We count page views and action names, anonymous browser IDs, referring domain, campaign channel and device class. We do not collect your JSON, email text, playlists or complete referring URLs. Country is unknown unless supplied by a trusted server configuration. Browser storage may be unavailable; in that case unique-user counts are limited to this visit.