Custom header is missing when sending emails in MIME format

Question

E-mails sent with our software contain a custom header that is evaluated by the recipient if he uses the same software.

So far we haven't had any problems sending with EWS or the Graph JSON API. But when emails are sent via Graph in MIME format, we noticed a strange behavior:
If an e-mail containing the custom header was sent with a mailbox via EWS or the Graph JSON API, the custom header is also included when sending in Graph MIME format.

If the mailbox is new and emails are only sent in MIME format, the custom header is not included.

Answer 1

Hi @Gerald Consolidate

I would recommend you to raise a support case with Microsoft Graph, a Support Engineer will be able to assist you better. You can raise support ticket from
http://aad.portal.azure.com/ or https://admin.microsoft.com/#/support/requests.

Hope this helps.

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