I had similar issues recently when on McAfee VPN that I just started in December. Thought I'd post what worked for me. When on VPN, sometimes I could not send, but always received. It's Comcast ISP and Comcast.net email.
Identified the specific issue: when the VPN was set to 'fastest connection' or words like that, sometimes it would use a foreign location. Last week I saw that it said 'Toronto, Canada' as the location, and it would not send. Sometimes it would say NY or Virginia and emails would send.
So I set the VPN to be USA location and it has worked fine now for a week.
Not sure if that was the fix, or if it was something else because i had been revisiting email account settings in Outlook via Microsoft 365 when it would not send. That said, since tweaking the McAfee VPN location it has worked just fine.
BruceW
Gold Problem Solver
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26.5K Messages
5 years ago
We'd need the text that goes along with the error code, as 421 is associated with several different error conditions, ex:
See https://postmaster.comcast.net/smtp-error-codes.php#421.
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BruceW
Gold Problem Solver
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26.5K Messages
5 years ago
CSI in the error message means the listed IP is blocked by Cloudmark Sender Intelligence. 172.102.178.157 is assigned to Ellijay Telephone Company / ETC Communications (see https://whois.arin.net/rest/net/NET-172-102-160-0-1). Please see https://forums.xfinity.com/t5/Email-Web-Browsing/Can-t-Send-Emails-from-PC-or-Phone-App/m-p/3355422#M219767. Are you using a VPN?
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Jarita
New Poster
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3 Messages
5 years ago
not using VPN
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BruceW
Gold Problem Solver
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26.5K Messages
5 years ago
Are you trying to send while using another ISP?
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D_Reynolds
New Poster
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1 Message
4 years ago
I had similar issues recently when on McAfee VPN that I just started in December. Thought I'd post what worked for me. When on VPN, sometimes I could not send, but always received. It's Comcast ISP and Comcast.net email.
Identified the specific issue: when the VPN was set to 'fastest connection' or words like that, sometimes it would use a foreign location. Last week I saw that it said 'Toronto, Canada' as the location, and it would not send. Sometimes it would say NY or Virginia and emails would send.
So I set the VPN to be USA location and it has worked fine now for a week.
Not sure if that was the fix, or if it was something else because i had been revisiting email account settings in Outlook via Microsoft 365 when it would not send. That said, since tweaking the McAfee VPN location it has worked just fine.
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