Usage

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Usage

• Reply and the add-on adds originals automatically - or asks first, if enabled in Options.
• De-duplicated by filename; S/MIME parts are always skipped. Images embedded in the original message stay in the reply body, where Thunderbird puts them, and are not copied as files.
• Blacklisted attachments are also skipped (case-insensitive glob patterns matching filenames, not paths). See Configuration.

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What happens on reply

• Detect reply → list the original attachments → skip S/MIME and embedded images → optional confirm → add the eligible files (skipping duplicates).

Part type	Copied to the reply
S/MIME signature file smime.p7s	No
S/MIME MIME types (application/pkcs7-*)	No
Image the message body embeds by cid:	No (it is in the body)
Image marked Content-Disposition: inline	No (it is in the body)
Image with a Content-ID the body never references	Yes
Attached email (message/rfc822) with a filename	Yes
Regular file attachment with a filename	Yes

An image counts as embedded only when the original message actually references it, or when the sender explicitly marked it Content-Disposition: inline. A bare Content-ID header is not enough: several mail clients put one on every image part, including genuine attachments, and those must still be copied.

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Cross-reference

• Forward is not modified by design (see Limitations below).
• For reasons an attachment might not be added, see "Why attachments might not be added".

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Behavior Details

• Duplicate prevention: The add-on marks the compose tab as processed using a per-tab session value and an in-memory guard. It won't add originals twice.
• Closing and reopening a compose window is treated as a new tab (i.e., a new attempt is allowed).
• Respect existing attachments: If the compose already contains some attachments, originals are still added exactly once, skipping filenames that already exist.
• Exclusions: S/MIME artifacts and embedded images are not copied as files.
  • Filenames: smime.p7s
  • MIME types: application/pkcs7-signature, application/x-pkcs7-signature, application/pkcs7-mime
  • Embedded images: an image/* part the message body references by cid:, or one marked Content-Disposition: inline. It stays in the reply body; copying it as a file would duplicate it.
  • Attached emails (message/rfc822): treated as regular attachments if they have a filename; they may be added (subject to duplicate checks and blacklist).
• Blacklist warning (if enabled): When candidates are excluded by your blacklist, the add-on shows a small modal listing the affected files and the matching pattern(s). This warning also appears in cases where no attachments will be added because everything was excluded.

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Keyboard shortcuts

• Confirmation dialog: Y/J = Yes, N/Esc = No; Tab/Shift+Tab and Arrow keys cycle focus.
  • The "Default answer" in Configuration sets the initially focused button.
  • Enter triggers the focused button. Tab/Shift+Tab and arrows move focus for accessibility.

Keyboard Cheat Sheet

Keys	Action
Y / J	Confirm Yes
N / Esc	Confirm No
Enter	Activate focused button
Tab / Shift+Tab	Move focus forward/back
Arrow keys	Move focus between buttons
Default answer	Sets initial focus (Yes or No)

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Limitations

• Forward is not modified by this add-on (Reply and Reply all are supported).
• Very large attachments may be subject to Thunderbird or provider limits.
  • The add-on does not chunk or compress files; it relies on Thunderbird's normal attachment handling.
• Encrypted messages: S/MIME parts are intentionally excluded.

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Why attachments might not be added

• Images the original message embeds are not copied as files. They are already in the reply body, where Thunderbird put them. See Configuration.
• S/MIME signature parts are excluded by design: filenames like smime.p7s and MIME types such as application/pkcs7-signature or application/pkcs7-mime are skipped.
• Blacklist patterns can filter candidates: see Configuration; matching is case-insensitive and filename-only.
• Duplicate filenames are not re-added: if the compose already contains a file with the same normalized name, it is skipped.
• Non-file parts or missing filenames: only file-like parts with usable filenames are considered for adding.

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See also

• Configuration