Gmail See's One User's Email Out of 20 as SPAM

Strange, I have one user out of 20 that all her emails sent to gmail go to the recipients SPAM. Other emails are fine. Nobody else out of 20 users has this issue.

2016 Server Standard with 2 VM's, one exchange and the other the PDC. Exchange 2016 on premise.
LVL 17
WORKS2011Managed IT Services, Cyber Security, BackupAsked:
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Iamthecreator OMIT Admin/EE Solution GuideCommented:
Has the recipient tried to mark her emails as NOT SPAM and adding the address to her contact list?
WORKS2011Managed IT Services, Cyber Security, BackupAuthor Commented:
Yes and if they do it doesn't happen again. This resolves the problem as a short term solution but it's obviously not a permanent one. He's getting emails returned three to four days later from people thats new responding using Gmail. This is a law firm and quite allot of people that respond to their website for first time inquiries use a gmail address. When she responds back she ends up in their spam folder and doesn't hear from them until they figure it out.

This is only happening to one user out of 15. Interesting he does use spammy like subject lines do to his business, it's a tax/irs firm so you can imagine they're already high on the probability list when inspected by filters. Interesting it just started happening.

I thought it may be an app but haven't found anything out of the ordinary.
WORKS2011Managed IT Services, Cyber Security, BackupAuthor Commented:
Resolved this by setting up a smart host.

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