每当我尝试连接到我的 Dovecot IMAP 服务器时，它都会给我一条消息，表明身份验证失败。此消息来自/var/log/mail.log文件：
Feb 7 15:22:17 celestine dovecot: imap-login: Disconnected (auth failed, 1 attempts in 2 secs): user=<celestine>, method=PLAIN, rip=::1, lip=::1, TLS, session=<QsPvvtbx5AAAAAAAAAAAAAAAAAAAAAAB>
我尝试连接 Roundcube 网络邮件程序，在 IMAP 日志中它显示以下内容：
[07-Feb-2014 15:22:15 -0500]: [A4F2] S: * OK [CAPABILITY IMAP4rev1 LITERAL+ SASL-IR LOGIN-REFERRALS ID ENABLE IDLE AUTH=PLAIN] Dovecot ready.
[07-Feb-2014 15:22:15 -0500]: [A4F2] C: A0001 ID ("name" "Roundcube" "version" "0.9.5" "php" "5.4.4-14+deb7u7" "os" "Linux" "command" "/")
[07-Feb-2014 15:22:15 -0500]: [A4F2] S: * ID NIL
[07-Feb-2014 15:22:15 -0500]: [A4F2] S: A0001 …