Why are my emails not threaded?

Providers such as Gmail and Microsoft Exchange / Office 365 accounts handle threading, by default they manage this by the message Subject.

Nylas can assist in threading, when sending vie our API, with the in_reply_to, by passing this attribute it assist the provider in determining a relationship between messages.


If messages are not being threaded then please inspect the headers of all the messages, and ensure that there is a relationship between them:

  • First message has no in_reply_to
  • Second messaged uses the Header Message-ID of the first
  • Third message uses the Header Message-ID of the first or second


Nylas only syncs the messages and thread information as per the provider, if it's not threaded on the provider then it's a provider issue. If it's threaded on the provider but NOT on Nylas, then reach out to support.


For IMAP accounts only, Nylas handles email threading. Please create a support ticket for us to investigate further.




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