The version of sendmail that came with RHEL4 had these two lines in the /etc/mail/sendmail.cf file.
TRUST_AUTH_MECH(`EXTERNAL DIGEST-MD5 CRAM-MD5 LOGIN PLAIN’)dnl
define(`confAUTH_MECHANISMS’, `EXTERNAL GSSAPI DIGEST-MD5 CRAM-MD5 LOGIN PLAIN’)dnl
For most mail readers, this was ok, but PC-Pine had a lot of problems with it. Since we’re already using SSL to connect, I changed the lines to this:
TRUST_AUTH_MECH(`LOGIN PLAIN’)dnl
define(`confAUTH_MECHANISMS’, `LOGIN PLAIN’)dnl
Now, PC-Pine works as expected.