Exim's -bh option can be useful for testing server authentication configurations.
exim -bP authenticator_list exim -bP authenticators exim -bP authenticator <authenticator name>
NOTE: The data for the AUTH command has to be sent encoded in base 64.
Perl's MIME::Base64 can be used for Base64 encoding.
perl -MMIME::Base64 -e 'print encode_base64("user\@mytestdomain.com")' perl -MMIME::Base64 -e 'print encode_base64("password321")'