Are you using <a href="https://support.mozilla.org/kb/difference-between-imap-and-pop3">POP accounts</a>? Unlike IMAP accounts, the only copy of your pop mail is in your local Thunderbird profile. If you want to add a POP account to beta, your options are:
<a href="https://support.mozilla.org/kb/difference-between-imap-and-pop3">POP kontuak</a> erabiltzen duzu? IMAPeko kontuek ez bezala, zure POP postaren kopia bakarra Thunderbird zure profilean dago. Betari POP kontu bat gehitu nahi badiozu, zure aukerak hauek dira: