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:
Ydych chi'n defnyddio <a href="https://support.mozilla.org/kb/difference-between-imap-and-pop3">cyfrifon POP</a>? Yn wahanol i gyfrifon IMAP, mae'r unig gopi o'ch e-bost POP yn eich proffil Thunderbird lleol. Os ydych chi am ychwanegu cyfrif POP at y beta, eich dewisiadau yw: