Cisco ASA SMTP Banner Corruption

telnet test.mail.com
On port 25:
220 ***************************

On port 587:
220 test.mail.com ESMTP

This can cause delayed and undeliverable mail, especially for larger messages, such as those with attachments.
 
Easy and dummy way to fix

ASA(config)#policy-map global_policy
ASA(config-pmap)#class inspection_default
ASA(config-pmap-c)#no inspect esmtp
(old school PIX: no fixup protocol SMTP 25)

Right way (if we gonna fix only banner corruption):
N.B. Banner re-writen is a issue when we perform test via telnet MX.MAIL.COM 25
More info here: http://www.cisco.com/c/en/us/support/docs/security/asa-5500-x-series-next-generation-firewalls/113423-asa-esmtp-smtp-inspection.html

  policy-map type inspect esmtp new_estmp_inspect_map
    description Don't touch my banner
    parameters
      no mask-banner

  policy-map global-policy
    class class-default
      inspect esmtp new_esmtp_inspect_map
  service-policy global-policy global

the advantage instead of deactivating is, that you are still able inspect other criteria like:

    match sender-address length ..
    match mime filename length ..
    match cmd line length ..
    match cmd rcpt count ..
    match body line length ..
List of available (e)smpt commands can be found here: http://www.cisco.com/c/en/us/support/docs/security/ios-firewall/69309-smtp-esmtp-ios-fw.html
Some simple troubleshooting commands:
show ip inspect all
debug ip inspect smtp
Deeper-look-int-topic here: http://www.cisco.com/c/en/us/td/docs/security/asa/asa82/configuration/guide/config/inspect_basic.html#wp1224614