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9 Messages
POP3 SSL handshake delay causing Outlook timeouts (0x8004210A) — IPv6 path appears slow
The following problem began for me at approximately 7:40 PM MST February 2, 2026 and persists today (February 3, 2026 4:00 PM MST.)
Full disclosure - I had Copilot help with debugging this issue. After much work, it has arrived at a temporary solution for me. Below is the text that Copilot generated for me to describe the situation and solution:
Hello, I’m experiencing a persistent issue with the Comcast POP3 service that appears to be related to IPv6 latency or a slow POP3 cluster node. I’m hoping this can be escalated to the mail server operations team.
Summary of the issue
POP3 access to
pop3.comcast.netis extremely slow during the SSL handshake phase.The SSL handshake takes ~15 seconds before the server banner appears.
Outlook (Microsoft 365, Windows 11) times out with 0x8004210A during the “Receiving” phase.
My Android mail client connects normally, which suggests the server is up and the mailbox is healthy.
Forcing a specific IPv4 address via the Windows hosts file immediately resolves the issue.
This strongly suggests the IPv6 path or a specific POP3 cluster node is slow or unresponsive.
Technical details
Testing from Windows Subsystem for Linux:
openssl s_client -connect pop3.comcast.net:995The connection succeeds, but the server banner is delayed by approximately 15 seconds before responding with +OK.
When Outlook attempts the same connection, it times out before the handshake completes.
What resolves the issue
If I force Outlook to use a specific IPv4 address by adding a hosts file entry such as:
96.118.253.108 pop3.comcast.netthen POP3 access works immediately and consistently. This confirms that the issue is not with my Outlook profile, password, or local configuration.
What this suggests
The behavior is consistent with:
A slow or degraded IPv6 route to the POP3 cluster, or
A specific POP3 server node in the rotation that is responding very slowly during SSL negotiation.
Request
Could this be escalated to the Comcast mail server engineering team to check:
IPv6 routing and latency to the POP3 cluster
Health and responsiveness of the POP3 nodes currently serving my region (Lafayette, CO)
Whether a specific node is experiencing SSL handshake delays
I can provide timestamps, traceroutes (IPv4 and IPv6), and additional OpenSSL logs if needed.
Thank you for your help — this appears to be a server‑side performance issue rather than a client configuration problem.
JimPColorado
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9 Messages
3 hours ago
Upon further review, this was potentially due to an issue with the cable modem (my own, not provided by Comcast/Xfinity) as other Android apps using Wi-Fi on my home network occasionally failed to connect to servers at the same time as my Outlook connection issue. (E-mail was not an Android app that failed, though.)
Switching to 5G solved the Android connection problems, which indicated a problem either at the router or modem.
Rebooting the cable modem has restored functionality on all devices and I no longer need the modified hosts file on my Windows 11 PC.
It is possible that the DNS cache on the router was stale and had not been refreshed recently.
Some Android apps also may use IPv6 instead of IPv4 and an IPv6 malfunction in the router could also explain the observed behavior.
A NAT table issue could have been another cause on the cable modem.
For anyone playing along at home, here are steps to diagnose the differences if you run into this problem, too.
On Windows:
1)
nslookup pop3.comcast.netIf it hangs or returns inconsistent IPs, DNS was the culprit.
2)
ping -6 pop3.comcast.netIf IPv6 stalls but IPv4 works, the modem’s IPv6 stack was the issue.
3)
Check NAT table exhaustion (indirectly)
If many apps fail simultaneously but existing connections continue, NAT is a likely cause.
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