Default signature placement creates cluttered email threads and breaks signature stripping

Checklist

• I have used the search function to see if someone else has already submitted the same bug report.
• I will describe the problem with as much detail as possible.

App

Thunderbird for Android

App version

10.0

Where did you get the app from?

F-Droid

Android version

Android 15

Device model

Nothing Phone 1

Steps to reproduce

Hi,

Thunderbird for Android allows users to configure a signature that is always appended to emails when they're sent from that particular account. Signatures are configured under "Settings -> select your account -> Sending mail -> Composition defaults". However, the signature is appended to the wrong part of the message body.

This is because the default configuration for signature placement is "Settings -> select your account -> Sending mail -> Composition defaults -> After quoted message"

What this means in a real life scenario is that if the user has an ongoing email thread with several earlier correspondences, and they reply from their mobile into that thread today, their signature is put at the very bottom at the entire thread after everybody's every reply.

I can list at least 4 reasons why this doesn't make sense:

• Nobody reads the bottom line of a long email thread with several replies. Essentially this behaviour makes signatures invisible to recipients.
• After a few replies, the bottom lines of the email thread will be nothing but a bunch of signatures one after another, as seen on the attached screenshot. Additionally, signatures get mixed and recipients won't be able to tell which signature belongs to which correspoindence.
• Signatures lose their contextual connection to the actual message they belong to.
• No sane user would expect signatures to work this way :)

Additionally, this breaks the "Settings -> select your account -> Sending mail -> Strip signatures on reply" functionality. Even with that feature enabled, signatures are not stripped from replies as I guess we can't find them where they are supposed to be.

I recommend that we make 'Before quoted message" the default behaviour for account signatures and perhaps remove "After quoted message" altogether. Alternatively, if we don't remove "After quoted message" because it covers some special use case, fix "Strip signatures on reply" to work with this option.

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Incorrect behaviour with the default "After quoted message""

Correct behaviour with "Before quoted message"

Expected behavior

Place signatures right after the new reply content but before the quoted previous messages, as seen with 'Before quoted message" enabled.

Actual behavior

The current default is "After quoted message" which doesn't make any sense in most real world scenarios, if ever.

Logs

Don't think logs would help anything here, but happy to provide them if required for the fix.

Start at the account-level Composition defaults for signature placement and the Strip signatures on reply behavior described in the issue. Reproduce a reply in a multi-message thread with an account signature, then verify that the signature appears before quoted content and is removed when stripping is enabled.