Sidmouth Hotels had a problem where their emails that were generated from Hotel Perfect were'nt sending. Hotel Perfect use 365 account for their mail, so if its ALL email and not just Hotel Perfect (Sidmouth Hotels might have to check that first) check security settings on 365 Admin:

- Go into Security Admin Center on 365

- Under More resources, click on Office 365 Securtity & Compliance

- Go to Threat Management

- Select Review

- Select Restricted Users

- If listed in there as High Threat, unblock (as long as you're sure email isnt compromised)

This happened we believe because of high mailbox usage, massive increase in outbound mail caused it to appear as spam