Well, I "copied" a folder with about 1600 emails to a gmail folder and only copied about 900 messages one time. Then I deleted the messages from the gmail folder and tried again. This time it only copied about 700. Since I don't run this laptop with offline storage, it appears that the messages are successively fetched from the source imap folder. Then at some point there is a problem and in the status bar I see something about trying to reconnect. At that point I think the partial folder content, which is probably concatenated into an mbox-like temporary file, is imap appended to the gmail folder, which happens quickly. I need to look closer at what is happening using imap:5 log and/or wireshark, but in any case, there is definitely a problem here and I understand all the complaints.
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Well, I "copied" a folder with about 1600 emails to a gmail folder and only copied about 900 messages one time. Then I deleted the messages from the gmail folder and tried again. This time it only copied about 700. Since I don't run this laptop with offline storage, it appears that the messages are successively fetched from the source imap folder. Then at some point there is a problem and in the status bar I see something about trying to reconnect. At that point I think the partial folder content, which is probably concatenated into an mbox-like temporary file, is imap appended to the gmail folder, which happens quickly. I need to look closer at what is happening using imap:5 log and/or wireshark, but in any case, there is definitely a problem here and I understand all the complaints. Edit: Doing this while recording IMAP:5 log, I see that the each email is fetched from the source folder in ascending UID order and immediately appended to the destination folder. So the order is fetch, append, fetch, append ... Looking at the log, I see that somehow the connection to the source server is lost. Can't tell from the log why or who is initiating the disconnect, tb or the server. This time over 1000 emails were fetch and appended before the problem occurred. I then transferred a small folder having offline store to gmail. With source offline store, nothing is fetched from the source server. Each message is just read from the mbox file and individually appended. So there is less to go wrong when you have offline store. Anyhow, given this info, I need to peruse WADA's detailed posts above and see what they say.