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As defined in the ZCS 7 Attributes page, zimbraSmtpHostname is the MTA or set of MTAs that a Zimbra ZCS mailstore uses to send outbound email:

<attr id="97" name="zimbraSmtpHostname" type="astring" max="256" cardinality="multi" optionalIn="globalConfig,server,domain" flags="serverInherited" callback="ServerConfig">
  <desc>the SMTP server to connect to when sending mail</desc>


In Bug 36173 [1], implemented in ZCS 6.0, this attribute was made a multi attribute, allowing multiple MTAs to be configured for redundancy.


For redundancy purposes, multiple MTAs should be running actively. For example, in a redundant environment, a minimum of two MTAs would be available:



By default, the zimbraSmtpHostname value is configured at the Server level. It can also be configured at the GlobalConfig or Domain level. To view your currently configured MTAs:

zmprov gcf zimbraSmtpHostname
zmprov gs `zmhostname` zimbraSmtpHostname   # do this on each mailstore server
zmprov gd example.com zimbraSmtpHostname      # do this for each active domain

To configure redundantly, additional MTAs must be added to the list. For example, at the Server level:

# su - zimbra
$ zmprov ms `zmhostname` +zimbraSmtpHostname mta1.example.com
$ zmprov ms `zmhostname` +zimbraSmtpHostname mta2.example.com
$ zmprov ms `zmhostname` +zimbraSmtpHostname mta3.example.com

or at the GlobalConfig level (since the Server level will override the GlobalConfig level, the Server level should be empty in order to use the GlobalConfig):

# su - zimbra
$ zmprov mcf +zimbraSmtpHostname mta1.example.com
$ zmprov mcf +zimbraSmtpHostname mta2.example.com
$ zmprov mcf +zimbraSmtpHostname mta3.example.com

or at the Domain level:

# su - zimbra
$ zmprov md example1.com +zimbraSmtpHostname mta1.example.com
$ zmprov md example2.com +zimbraSmtpHostname mta2.example.com
$ zmprov md example3.com +zimbraSmtpHostname mta3.example.com


  1. Be sure that all outbound MTAs allow "relaying" for all mailstores, in order for outbound messages to non-local domains to be successfully relayed. Confirm that the zimbraMtaMyNetworks configuration is correct to include all local, trusted IPs.
Verified Against: unknown Date Created: 4/12/2012
Article ID: https://wiki.zimbra.com/index.php?title=ZimbraSmtpHostname Date Modified: 07/11/2015

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