Imceainvalid on sent emails - Outlook 2013 and Exchange 2013 on premise

Hi All
I have a customer that has had a ongoing issue for some time now and I have had no luck in resolving it. I can see the exact same issues highlighted by other people but generally this relates to older office version and/or older exchange.
Issue: Error after sending email:
IMCEAINVALID -
Remote Server returned '550
5.1.0 RESOLVER.ADR.InvalidInSmtp; encapsulated INVALID address inside an SMTP
address (IMCEAINVALID-)'
[email protected]
Cause:
If you check the properties of the To/CC addresses (only the display name is filled out as the email address, the email address field itself and "type" are not filled (does not always occur and not for ALL
recipients of email)
Checks:
There are no local contacts for these email addresses in outlook. The auto complete cache has also been cleared. Running exchange in cached mode is not an available option due to the setup.
Email details:
These emails are generated by third party software however not the same software. This is occurring on emails generated into the outlook client by software Rosetta as well as by Mimecast plugin to download archivedemails(then reply to all). This is also
an intermittent issue and does not occur every time with all the emails.
Search:
All searches I have done seem to mainly point to the auto complete option in outlook but this is not the cause of this in my scenario. There was also a known issue in Office 2007 I believe with a office update to resolve, but this is Outlook 2013.
Any assistance would be appreciated.
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Reply

Hi,
If you just create an email directly from Outlook, has this issue occurred ever?
You can also start Outlook in Safe Mode and then use the 3rd-party software to send some test emails, check if the problem persists.
To start Outlook in Safe Mode:
Press Win + R, type "outlook.exe /safe" in the blank box, press Enter.
In Outlook Safe Mode, all add-ins will be disabled. If there's no problem in Outlook Safe Mode, disable the suspicious add-ins to verify which one caused the problem.
Since the issue is intermittent, you may need to test for a period.
Regards,
Melon Chen
TechNet Community Support
It's recommended to download and install
Configuration Analyzer Tool (OffCAT), which is developed by Microsoft Support teams. Once the tool is installed, you can run it at any time to scan for hundreds of known issues in Office
programs.