1. SPF/DKIM/DMARC Failures
When your server forwards an email (from Gmail, Yahoo, etc.) to another address:
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It re-sends the message without altering the sender.
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The receiving server (like Gmail) checks SPF/DKIM/DMARC for the original sender, not your server.
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Because the mail came from your server's IP, but claims to be from someone else, SPF and DMARC can fail, and the forwarded message can be rejected or marked as spam.
❗ This can result in emails being silently dropped, blackholed, or bounced.
2. Your Server Can Be Blacklisted
If spam is forwarded through your server (even unknowingly):
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Your IP address can be blacklisted (RBL).
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Mail to Microsoft (Outlook/Hotmail), Gmail, Yahoo, etc. may bounce or be delayed.
3. Looping or Excessive Forwarding
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Poorly set up forwarders can create mail loops.
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Forwarding to auto-responders or aliases can cause flooding.
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Forwarding spam to other servers could violate their policies.
4. No Accountability or Logging
When spam is forwarded:
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The recipient can't tell it was forwarded from your server.
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It looks like your server sent spam, even if it didn’t originate it.
