I transferred my email setup to a new laptop, and fetchmail stopped fetching my mail.  From what I can tell in the fetchmail log, it authorizes fine, sees that new emails are there, tries to fetch them, and fails due to a persistent Temporary lookup failure - here's the relevant log bit:fetchmail: 2134 messages (2130 seen) for recent:patena at pop.gmail.com (397667985 octets).fetchmail: POP3> LIST 2123fetchmail: POP3< +OK 2123 679fetchmail: POP3> RETR 2123fetchmail: POP3< +OK message followsfetchmail: reading message recent:patena@gmail-pop.l.google.com:2123 of 2138 (679 octets)Trying to connect to 127.0.0.1/25...        connected.fetchmail: SMTP< 220 bleen.gateway.2wire.net ESMTP Postfix (Ubuntu)fetchmail: SMTP> EHLO bleenfetchmail: SMTP< 250-bleen.gateway.2wire.netfetchmail: SMTP< 250-PIPELININGfetchmail: SMTP< 250-SIZE 307200000fetchmail: SMTP< 250-VRFYfetchmail: SMTP< 250-ETRNfetchmail: SMTP< 250-STARTTLSfetchmail: SMTP< 250-ENHANCEDSTATUSCODESfetchmail: SMTP< 250-8BITMIMEfetchmail: SMTP< 250 DSNfetchmail: SMTP> MAIL FROM:<patena@gmail.com> SIZE=679fetchmail: SMTP< 250 2.1.0 Okfetchmail: SMTP> RCPT TO:<weronika@localhost>fetchmail: SMTP< 451 4.3.0 <weronika@localhost>: Temporary lookup failurefetchmail: SMTP error: 451 4.3.0 <weronika@localhost>: Temporary lookup failurefetchmail: SMTP> RSETfetchmail: SMTP< 250 2.0.0 Okfetchmail:  not flushedfetchmail: POP3> LIST 2124(And so on from LIST to not flushed for each unseen message.)It's been going on for most of a day, so this temporary lookup failure doesn't seem very temporary.
fetchmail sees mail but doesn't fetch it - persistent temporary lookup failure
email;fetchmail
The fetchmail: SMTP ... logs indicate that fetchmail is talking to a Mail Transport Agent (MTA), here Postfix, and Postfix has rejected the message from fetchmail on account of not being able to resolve the (unqualified!) hostname of localhost. Thus, the solution is to correct the DNS (and possibly hostname) for the system. This may also make sending mail from the system easier, as many mail servers will reject mail from hosts with unqualified names as an anti-spam measure.An alternative would be to configure fetchmail via the mda setting to instead deliver directly to a program such as maildrop, thus cutting the local MTA out of the delivery loop.