Bugzilla

> Could it be that the issue I was experiencing before was just TB downloading some of the messages with large attachements, even though it previously thought it had already syncronized everything?

Theoretically large attachments shouldn't cause a problem when you store messages locally in mbox file and for offline use. The only "problem" I've seen is if you don't store messages locally for offline and your attachment is too large (maybe >25M, don't remember the exact figure), there may not be enough ram allocated to hold the message (or the attachment part of the message) and you see something like a 27 byte file saved when you try to save the attachment. But that's not your issue.

>I've now selected 'When I delete a message: Just mark it as deleted' in server settings, as suggested.
(This way deleted messages do not appear in Trash folder.)

With gmail imap at default setting at gmail.com, when you delete a message in tb which just sets the \deleted flag on the message if you are set to "just mark as deleted", this causes gmail to immediately expunge the message from the folder. If you have one or more folders with the same message, when you delete it from the last folder it still remains in "All Mail". So if you are not subscribed to "All Mail" and you want to get back a deleted message, you will have to go to gmail.com and copy the message back from "All Mail" to where you want it. 

With all other non-gmail servers, when you mark a message \deleted it just leaves it where it is (doesn't expunge it automatically) and tb continues to show it but with an X in front and with a strike-through line. With gmail you may see this too but either temporary or the message won't be readable, not sure, since the message was auto-expunged.

You can change default  gmail.com setting so that it doesn't auto-expunge when you mark the message as \deleted so the deleted messages remain present in the folder but just crossed out and are only expunged from the folder when you do a "compact". However, changing this at gmail.com my cause other issues, not sure (I'm not a big gmail user, but have a couple accounts mostly for testing).

> Could it be that the issue I was experiencing before was just TB downloading some of the messages with large attachements, even though it previously thought it had already syncronized everything?

Theoretically large attachments shouldn't cause a problem when you store messages locally in mbox file and for offline use. The only "problem" I've seen is if you don't store messages locally for offline and your attachment is too large (maybe >25M, don't remember the exact figure), there may not be enough ram allocated to hold the message (or the attachment part of the message) and you see something like a 27 byte file saved when you try to save the attachment. But that's not your issue.

>I've now selected 'When I delete a message: Just mark it as deleted' in server settings, as suggested.
(This way deleted messages do not appear in Trash folder.)

With gmail imap at default setting at gmail.com, when you delete a message in tb which just sets the \deleted flag on the message if you are set to "just mark as deleted", this causes gmail to immediately expunge the message from the folder. If you have one or more folders with the same message, when you delete it from the last folder it still remains in "All Mail". So if you are not subscribed to "All Mail" and you want to get back a deleted message, you will have to go to gmail.com and copy the message back from "All Mail" to where you want it. 

With all other non-gmail servers, when you mark a message \deleted it just leaves it where it is (doesn't expunge it automatically) and tb continues to show it but with an X in front and with a strike-through line. With gmail you may see this too but either temporary or the message won't be readable, not sure, since the message was auto-expunged.

You can change default  gmail.com setting so that it doesn't auto-expunge when you mark the message as \deleted so the deleted messages remain present in the folder but just crossed out and are only expunged from the folder when you do a "compact". However, changing this at gmail.com may cause other issues, not sure (I'm not a big gmail user, but have a couple accounts mostly for testing).