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Sending email to Gmail accounts

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I keep getting "Undelivered Mail Returned to Sender" messages when sending emails from Thunderbird to Gmail accounts. Can you help? I am using Thunderbird 102.11.2 (32-bit) as POP mail server with email account through pairserver.com (SSL/TSL with normal password). I can send to Gmail accounts with no trouble directly from webmail.pair.com.

I keep getting "Undelivered Mail Returned to Sender" messages when sending emails from Thunderbird to Gmail accounts. Can you help? I am using Thunderbird 102.11.2 (32-bit) as POP mail server with email account through pairserver.com (SSL/TSL with normal password). I can send to Gmail accounts with no trouble directly from webmail.pair.com.

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Is that the complete message? If there is more content, that may help. It may be that the sending IP is blacklisted, as your IP is different from your web host.

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Chosen Solution

Is that the complete message? If there is more content, that may help. It may be that the sending IP is blacklisted, as your IP is different from your web host.

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Thanks. I read the message more closely after receiving your reply, and I think it was an authentication issue. Seems to be working now.

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My son seems to have found a solution. This is part of his email

"The tag has been added onto the DNS" and further "it's a known change google did".

I don't understand but the fix seems to work. Good luck out there.