Tenant to Tenant Mail send as permission

[Marsh7979]

Hi All,

We are engaging a third party company who will be processing email requests on our behalf. The idea was to have a forwarder set to forward the support calls onto the third party and then add their mail server to our SPF record to allow them to send as our domain. 

It turns out , the third party company are also on Office 365,so I assume we won't need to add anything to our SPF. As both sides are on Office 365 ,I have a few questions:

1. How can we authorise the other tenant to send on our behalf if both sides mail server is Office365?

2. Am I missing any features within Office 365/Exchange online that makes this scenario easier to implement?

Many Thanks

[#2]

1) You can only connect a single e-mail domain to a single Office 365 tenant; a tertiary (sub)domain is perhaps more ideal, for sake of routing bulkmail and seperating mail flow.
2) That said, bulkmail is limited in 365 (there are limits in message sending/no. of recipients/etc). So, usability for your scenario depends on volume. If not, you (they) may need to look at 3rd parties.

More info in EOP limitations, see https://docs.microsoft.com/en-us/office365/servicedescriptions/exchange-online-protection-service-de...