New attachment replacing large file when editing email as new renders email not to be sent

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

8.1

Where did you get the app from?

Google Play

Android version

14

Device model

Galaxy Fold 4

Steps to reproduce

Pre-conditions:
Be logged with at least one account.

Steps:

1. Launch TB.
2. Compose a new email and attach a large file (in my case app-thunderbird-full-debug.apk= 32.8MB)
3. Send email to desired contact.
4. Failed to send some messages-Message too large for server notification is received, tap on it.
5. In the outbox section, select said email with large attachment.
6. Tap on email options and select Edit as new message
7. Delete large attachment and select a new, smaller attachment (a jpg file, in my case)
8. Send Email

Expected behavior

The large attachment is successfully replaced by the new attachment, the email is successfully sent and not fail notifications are displayed anymore.

Actual behavior

The email containing the new attachment is not sent/received, the fail to send some messages notification is displayed and the old(large) attachment is the one displayed in Outbox.

Logs

https://github.com/user-attachments/assets/4b51dca1-3e57-4a6c-84a1-8db22361207a

Start by reproducing the failure in Thunderbird for Android 8.1 using the listed outbox and Edit as new steps, then inspect the attachment replacement flow. Done means deleting the oversized attachment, adding a smaller one, and sending successfully without the old attachment or failure notification.