If you're getting a response from emails sent from Tern that "A message that you sent could not be delivered to one or more of it's recipients" and that it's due to a SMTP error from the remote mail server this article will help you troubleshoot.

Generally, these errors are not caused by Tern. Instead, they're generally related to your global email configurations.

Starting February 1st 2024, Google has turned on enforcement of two technologies to protect users from spam. They are called DKIM and SPF. They are used to make sure that the person sending from a domain name actually owns that domain.

Tern's email provider does not require special DMARC / DKIM / SPF configuration. However, improper configuration can lead to issues with Tern.

Reason: Most providers have two sending servers (SMTP) one for their mail clients another for third party applications such as Tern. If you have no issues sending from you regular email, but get these errors when sending from Tern... The bulk sending server may not have been included.

Solution: As per the Google linked article in the bounce response, have the customer reach out to the provider to determine what IP's to add to the SPF /DKIM records for their non webmail SMTP servers.

Specifically, make sure that if your email provider has multiple records that must be included in your domain configuration that you've added those.