Understanding the EX to SMTP conversion issue
You’ve migrated your items to a new server / cloud using the CodeTwo migration software. Now, when you reply to an email, in the To field, instead of a regular email address of your recipient, you see a number of tags with values similar to the ones presented below:
</o=Example/ou=Exchange Administrative Group (FYDIBOHF23SPDLT)/cn=Recipients/cn=<string of numbers>-user's name>
The issue is not caused by the CodeTwo software but inability to properly convert legacy EX addresses to SMTP ones due to a missing set of MAPI properties (e.g. SMTPAddress) in the source items.
By default, items on a source Exchange server use the legacy EX addresses (even if a sender/recipient actually has an email address defined). So, if you attempted to migrate them using e.g. in-built methods offered by Exchange Web Services (EWS) API, you would face the similar issue in your target environment as described in the Problem section.
On the other hand, the CodeTwo migration software allows you to convert the legacy EX addresses to the SMTP ones (not the other way round) during migration. Thanks to that, you can reply to emails using regular email addresses in the target environment. When you experience the issue described above, it does not mean that the CodeTwo software altered your items in any way but was just not able to complete the EX to SMTP conversion. It’s also worth mentioning that the conversion itself is actually an internal part of the entire migration process, so there is no other way to resolve the issue but to repeat the migration process (once the root cause has been eliminated).
As stated above, the core reason for the issue is a missing set of MAPI properties of your source items. Because of the missing data, the conversion mechanism integrated into CodeTwo software is not able to convert legacy addresses to SMTP. The best idea to check which MAPI properties may be missing is to compare properties of an unproblematic item with a problematic one, e.g. using the OutlookSpy add-in for Outlook.
To sum up, the root cause of the issue lies in the source server environment – missing MAPI properties (e.g. SMTPAddress). Consequently, the easiest way to ensure proper migration is to delete the problematic mailboxes on the target server, define the properties of their source items and, finally, restart the migration process with the CodeTwo software.