Office 365 email - Emails in Sent folder are duplicated

Microsoft Office 365 added duplicate emails in Sent folders for SMTP relay solutions September of 2018.

https://office365.uservoice.com/forums/264636-general/suggestions/17035333-smtp-relay-via-office-365-keep-copy-in-sent-item

https://blogs.technet.microsoft.com/exchange/2018/04/20/changes-coming-to-the-smtp-authenticated-submission-client-protocol/

Please refer to SendGrid.com as an alternate solution for the SMTP relay if the duplicate emails are an issue.