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:
您是否在使用 <a href="https://support.mozilla.org/kb/difference-between-imap-and-pop3">POP 账户</a>？与 IMAP 账户不同，POP 邮件仅有一份副本，位于 Thunderbird 本地配置文件中。如果您想在测试版中添加 POP 账户，可以选择：