remove exchange 2013 server from routing

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Occasional Visitor

Hi guys, 
Currently working on migrating some legacy exchange servers into AWS and I'm struggling to work out why mail is still routing through one. for context all mailboxes have been running in 365 for years, however both servers still run both MB & CAS roles. both servers also exist in the same AD site. 

 

All our internal devices use smtp.domain.com for their smtp relay which was a DNS round robin between the two exchange servers EX01 and EX02. the record for EX01 was removed. EX01 was also removed from all send connectors. 

I'm still seeing logs, but it all looks like EX02 -> EX01 -> EX02 -> Destination. This isn't for all email either, seems to be roughly 50%. 
The last version of Exchange I worked on was 2010 so there may be some fancy features I'm not aware of here :)

TIA. 

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