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How to set up a distributed domain on IceWarp

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Petr Štěrba
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The distributed domain is a popular solution for businesses with multiple locations. If you wish to distribute your IceWarp email servers around your locations, each with a group of your users, follow the steps below:

HOW TO SET IT UP

  • Set up the IceWarp Server at each location

  • Set up a distributed domain Type on each server. Each domain should have the same name (i.e. all domains have the name mydomain.com) (Domain - Options)

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  • Set up an MX record for each server in the distributed domain (if you do not know how to set up DNS, please look at this article).

  • Enter all related distributed domains' internal or external IP addresses into the Value field. Separate the IP addresses by semicolons. (Field should contain the IP addresses of the other servers in the distributed domain or can be left blank if MX DNS records are defined for all domains in the distributed system)

  • Set up Verification to Use RCPT TO command

HOW IT WORKS

When a message is delivered to the receiving server, it will:

  • Use the SMTP VRFY or RCPT command on all other servers in the distributed domain to locate the message recipient. This is not needed if the user is local to this instance. See the Verification option further.

  • If the user is not found, the message is rejected. In this case, the sending server receives a 5xx permanent error.

  • If any of the servers in the distributed system cannot be contacted and none of the other servers (that can be contacted) has the appropriate recipient, then a 4xx temporary error is reported to the sending server. In this case, the sending server should retry after a period of time.

  • If the user is found, then any IceWarp Antivirus and AntiSpam processing is performed (if enabled), and the message is delivered to the user. This processing goes on the machine where the user is created.

An important difference between a distributed domain and a backup domain is how they respond when they cannot connect to the receiving server:

  • A backup domain will save and deliver the message when the server is back online.

  • A distributed domain will send a 4xx warning to the sending server, which then tries to send the message again later.

VERIFICATION

Distributed domains require recipient real-time verification. The email will not be sent out if one of the destination servers entered in the Value field is inaccessible. The user will get the "4xx – try again later" error in this case. The email will be sent when the destination server with the appropriate user account is available. For WebClient, there is a workaround – use Bounce back messages for failed recipients (Administrator Options - Mail - General). Another option is to use backup domains. However, you lose the IM/VoIP functionality of the distributed scenario.

ANTISPAM PROCESSING

Antispam is not performed for external recipients of distributed domains. This can be changed in the API console. Enter C_AS_BypassDistributedDomain and set the value to 0. In this case, Antispam is performed if it is set for outgoing messages. See the note to domain aliases and verification within the Backup domain field.

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