fetchmail, as the name indicates, fetches mails from other accounts, forwarding them to the local smtpd. Username-password-pairs for authentication are best kept inside a .netrc file, which is supported by fetchmail.

poll pop.provider.tld proto pop3
        user "blubusername"
        user "blub2username"

poll imap.provider.tld proto imap
        user "blubusername"
        ssl sslfingerprint "<fingerprint>"
        sslcertck
        sslcertpath /etc/ssl/certs/

The fingerprint is shown via:

fetchmail -vv

The IMAP server's certificate has to be saved using the following command:

openssl s_client -connect imap.provider.tld:995 -showcerts >/etc/ssl/certs/imap.provider.tld.pem

In the resulting file imap.provider.tld.pem you have to truncate

• everything before 'BEGIN CERTIFICATE' and
• everything after 'END CERTIFICATE'.

Then the SSL-hash has to be updated using:

c_rehash /etc/ssl/certs

Verify communication goes via SSL:

fetchmail -v

http://www.physik.uni-kiel.de/et/tiki/tiki-print_article.php?articleId=2