How to migrate mailboxes with x400 address to smtp addresses on Office 365

Microsoft Office 365 is steadily gaining ground as a business grade collaboration and email tool. More and more companies are also migrating from their on premise Exchange deployments to 365. As a result, we can observe that some of them encounter difficulties while making the move. One of these problems is conversion of the old X.400 email address standard, commonly used in the days of Exchange 2003 to the now widely used SMTP.

The X.400 standard is a set of recommended protocols for exchanging and addressing emails. Due to the fact that it describes much more message properties (such as country name, mail service provider, initials, surname, organization name, etc.) its address is quite long and complicated, as opposed to SMTP . E.g. an SMTP address like in the X.400 standard would be presented as: c=us;admd=codetwo;prmd=chicago;g=thomas;s=smith.

Due to its complexity X.400 was slowly replaced and ruled out by SMTP which is today’s email transfer standard. However, in old messaging systems, such as MS Exchange 2003 it is still present, which poses a problem when an organization wants to move to newer systems, such as Exchange 2010, 2013 or Office 365.

The issue with X.400 on latest systems is that these addresses are simply not supported and email clients are not able to recognize them as valid senders/recipients.

To fix this issue you need to convert all migrated users’ addresses to the SMTP standard. They can be changed manually, user-by-user if there is a small number of them. However, it is better to run the following PowerShell script in the EMS if the number of X.400 users is large:

$Recipients = Get-Mailbox -ResultSize Unlimited | Where {$_.EmailAddresses -like "X400:*"}
 foreach ($Recipient in $Recipients)
 [array]$AllEmailAddresses = $Recipient.EmailAddresses
 [array]$NoX400Addresses = $Recipient.EmailAddresses | Where {$_ -notlike "X400:*"}
 Set-Mailbox -Identity $Recipient.Identity -EmailAddresses $NoX400Addresses

Bear in mind that after migrating to Office 365 these addresses are unusable until they are converted, which might result with users not being able to send/receive messages.

Luckily, there is a tool that does the conversion on the fly, while migrating – CodeTwo Office 365 Migration. Instead of tedious manual editing or complicated PS scripting the whole process is simplified to clicking one option within the program’s settings – Address rewriting. Simply mark the Change EX addresses to SMTP addresses option and let the program do the rest.

The CodeTwo Office 365 Migration software is available free of charge – add CodeTwo as your partner in the Office 365 administration panel to receive the license.

How to migrate mailboxes with x400 address to smtp addresses on Office 365 by

2 thoughts on “How to migrate mailboxes with x400 address to smtp addresses on Office 365

  1. Hi there,
    After I exported a PST file, I found that email addresses were converted to 32 hex characters and some additional information:
    This is an example:
    cn=Recipients/cn=73ef4a460a8b46b585be9579f6c46abe-Alvaro Alfo

    Is there a way to get información in a less cryptical format? I would work fine with: /g=.. and s=…

    Thanks a lot.


    • Hi Antonio,

      Apologies for the late reply. What migration method did you use and from which Exchange version were you migrating?


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