I'm attempting to setup a postfix relay to our new Office365 setup for some internal devices on our network that require this specific setup. I've been trying various sites with configs and troubleshooting tips around the web for the better part of two days but I keep running in to the following error in /etc/log/mail.log when I attempt to send using: mail [email protected] Any help would be greatly appreciated.

Jun 19 05:41:16 smtphost postfix/smtp[1357]: warning: smtp.office365.com[]:587 offered null AUTH mechanism list
Jun 19 05:41:17 smtphost postfix/smtp[1357]: warning: SASL authentication failure: No worthy mechs found
Jun 19 05:41:17 smtphost postfix/smtp[1357]: 5E7A32034A: to=<[email protected]>, relay=smtp.office365.com[]:587, delay=7289, delays=7283/0.32/5.6/0, dsn=4.7.0, status=deferred (SASL authentication failed; cannot authenticate to server smtp.office365.com[]: no mechanism available)

Here is the ouput of my postconf -n

alias_database = hash:/etc/aliases
alias_maps = hash:/etc/aliases

append_dot_mydomain = no
biff = no
config_directory = /etc/postfix

inet_interfaces = loopback-only
inet_protocols = ipv4

mailbox_size_limit = 0

mydestination = smtphost, localhost.localdomain, localhost
myhostname = smtphost
mynetworks =
myorigin = /etc/mailname

readme_directory = no
recipient_delimiter = +

relayhost = smtp.office365.com:587

smtp_always_send_ehlo = yes
smtp_sasl_auth_enable = yes
smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
smtp_sasl_security_options = noanonymous, noplaintext
smtp_tls_CAfile = /etc/postfix/cacert.pem
smtp_tls_security_level = may
smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache
smtpd_banner = $myhostname ESMTP $mail_name (Debian/GNU)
smtpd_sasl_auth_enable = yes
smtpd_sasl_path = smtpd
smtpd_sasl_type = dovecot
smtpd_tls_cert_file = /etc/ssl/certs/ssl-cert-snakeoil.pem
smtpd_tls_key_file = /etc/ssl/private/ssl-cert-snakeoil.key
smtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scache
smtpd_use_tls = yes

here are the contents of my sasl_passwd file:

smtp.office365.com [email protected]:p@ssword
  • Does SASL authentication work when you connect to smtp.offic365.com with some other client using the same username and password?
    – Jenny D
    Commented Jun 19, 2013 at 7:42
  • Jenny D, yes it does work when using another client. I think the issue is on my end with my config.
    – misc
    Commented Jun 19, 2013 at 23:34

3 Answers 3


I had a similar problem and used 'smtp_tls_security_level = encrypt' to fix.

  • Attention: Docs: postfix.org/postconf.5.html#smtp_tls_security_level "encrypt": this security level is not an appropriate default for systems delivering mail to the Internet.
    – guettli
    Commented Jun 26, 2014 at 8:09
  • As long as you're only sending to O365, or you can otherwise trust that the receiving side supports TLS, 'smtp_tls_security_level = encrypt' is fine. the issue is that you cannot trust every receiving MX on the internet to support TLS.
    – blaughw
    Commented Jan 7, 2016 at 21:19

According to the this MS Knowledge base article You need a postfix 2.9 or later for relaying to work.

I ended up installing postfix-2.10.1 from source along with cyrus-sasl-2.1.25 (not dovecoat like you seem to be using in your setup) Since my distribution of choice has a to old postfix version in its repositories.

Using the following make flags taken from the postfix documentation here and here

make makefiles CCARGS="-DUSE_SASL_AUTH -DUSE_CYRUS_SASL -DUSE_TLS -I/usr/local/include/sasl -I /usr/local/include " AUXLIBS=" -lsasl2 -lssl -lcrypto"

I still get the message "offered null AUTH mechanism list" in my postfix mail log. But mails are delivered properly.

Note: Using email addresses that differ from the account email address (or alias) are rejected by the microsoft mail servers.

But you can change the FROM: field to whatever you like. If you find a way around this leave a comment.

  • Very interesting. Which of features in the postfix 2.9 will be used by Exchange?
    – ALex_hha
    Commented Jul 30, 2013 at 14:11
  • FYI - KB article link now broken :( Commented Jun 11, 2015 at 14:39

You need to make sure you've got SASL auth mechanisms installed:

yum install cyrus-sasl-plain cyrus-sasl-scram cyrus-sasl-md5  cyrus-sasl-ntlm

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