Why are emails being marked as spam when they're forwarded to Gmail addresses?

Email marketer from Reddit shares that the receiving email server will be using it's spam detection algorithms based on the mail server IP address. This means that if a email from the past hasn't been recieved from that mail server before it could be marked as spam.

Marketer from Email Geeks suggests high volumes of forwarded emails to Gmail could cause spam issues and questions the reasons for such forwarding.

Marketer from Email Geeks wonders what Gmail's threshold is for SPF/DKIM/TLS failures due to forwarding, as some breakage is inevitable.

Email marketer from Litmus suggests that emails can be marked as spam due to authentication issues. The forwarding process can sometimes break the authentication chain and give google reason to mark the email as spam.

Email marketer from EmailToolTester answers that forwarded emails not having the correct SPF and DKIM settings can cause issues with emails being sent to Gmail addresses. This is because Google cannot verify the emails authenticity.

Email marketer from SendPulse responds that Gmail uses reputation as one of its main determining factors in deciding if a email is spam or not. If a users domain has a bad reputation then forwarded emails will be marked as spam.

Marketer from Email Geeks explains that even forwarded email builds domain reputation, likely negatively in this case.

Email marketer from Neil Patel Blog explains that forwarded emails often lack proper authentication (SPF, DKIM, DMARC) on the receiving server (Gmail), making them look suspicious and more likely to be flagged as spam.

Email marketer from StackOverflow mentions that SPF records need to be correctly configured at each domain to allow forwarding, which will prevent the email being marked as spam.

Marketer from Email Geeks shares that not mailing specific domains is a red flag for abusive activities, unless there's a valid reason.

Email marketer from Email on Acid explains that forwarded emails might trigger Gmail's spam filters if they resemble list bombing attacks where a single email is sent to many recipients at once. Gmail may flag these forwarded emails as suspicious, especially if the forwarding behavior is unusual for the user's typical email patterns.

Email marketer from Mailjet responds that Gmail's spam filters are complex and consider many factors, including sender reputation, email content, and user engagement. Forwarded emails can be negatively impacted if the original sender has a poor reputation or if the content triggers spam filters.

Expert from Word to the Wise explains that forwarding can break authentication mechanisms like SPF and DKIM. Gmail relies on these to verify the sender's identity, and if they fail during forwarding, the email is more likely to be flagged as spam.

Expert from Spam Resource notes that forwarded email can trigger spam filters if the original sender's domain is on a blocklist or has a poor reputation. Forwarding doesn't remove this negative reputation, and it can affect deliverability to Gmail.

Documentation from DMARC.org explains that a strict DMARC policy (p=reject or p=quarantine) on the original sender's domain can cause forwarded emails to fail DMARC authentication at Gmail. This happens because the forwarded email's headers no longer align with the original sender's domain, leading Gmail to enforce the DMARC policy and potentially mark the email as spam or reject it.

Documentation from Google Workspace Admin Help shares that when emails are forwarded, Gmail sees the forwarder's server as the sender. If the forwarder's IP has a poor reputation or the original email failed authentication checks, Gmail might mark the forwarded email as spam. They suggest using authenticated mail.

Documentation from RFC Editor explains that when an email is forwarded the original headers aren't always preserved perfectly. If vital authentication headers are stripped or altered during forwarding, Gmail may not be able to verify the sender's authenticity, increasing the likelihood of the email being marked as spam.

Documentation from Return Path shares that the lack of engagement with forwarded emails might also play a role. Gmail uses engagement signals to determine whether emails are wanted by the recipient. If forwarded emails consistently receive no interaction (opens, clicks, replies), Gmail may start to filter them as spam.