Outlook Fails to Connect to IPV6-addressed MAPI Server

Question

I have an intermittent problem of Outlook timing out at startup, during the part where it tries to connect to my ISP’s MAPI server farm. Per the details below, I think the issue occurs when the ISP’s DNS presents my workstation with an IPV6 address instead of an IPV4 address for one of its MAPI servers. I have found some rumblings from past years in various forums with somewhat related observations about Outlook and IPV6 addressing, but nothing like an acknowledgement from Microsoft or any suggestions from them. Has anyone in this forum experienced a similar issue and do you have a solution other than setting your workstation to block IPV6 addressing?

Details…

I have used Outlook against my ISP’s MAPI/SMTP servers for years. On occasion, Outlook has timed out at start-up during the part where it communicates with a MAPI server to receive inbound mail and synchronize the folders. Usually, I have been able to just restart Outlook. But in the last few weeks, this problem has occurred so frequently that I had to look into it deeper.

I have run [Test Account Settings] in Outlook’s “POP and IMAP Account Settings” window when things are good and when things are bad. The following are excerpts from the associated log files in %Temp%\Outlook Logging.

During a good time, the log indicated that Outlook got an IPV4 address (96.118.19.10) and the test process ran successfully.

IMAP: 07:49:04 [db] Connecting to 'imap.comcast.net' on port 993.
IMAP: 07:49:04 [db] OnNotify: asOld = 0, asNew = 2, ae = 0
IMAP: 07:49:04 [db] srv_name = "imap.comcast.net" srv_addr = 96.118.19.10:993
IMAP: 07:49:04 [db] OnNotify: asOld = 2, asNew = 3, ae = 1
IMAP: 07:49:04 [db] OnNotify: asOld = 3, asNew = 4, ae = 0
IMAP: 07:49:04 [db] Negotiating secure connection with 'Microsoft Unified Security Protocol Provider'.
IMAP: 07:49:04 [db] OnNotify: asOld = 4, asNew = 6, ae = 2
IMAP: 07:49:04 [db] OnNotify: asOld = 6, asNew = 6, ae = 4
IMAP: 07:49:04 [db] OnNotify: asOld = 6, asNew = 5, ae = 2
IMAP: 07:49:04 [db] OnNotify: asOld = 5, asNew = 5, ae = 3
IMAP: 07:49:04 [rx] * OK [CAPABILITY IMAP4rev1 SASL-IR LOGIN-REFERRALS ID ENABLE IDLE LITERAL+ AUTH=PLAIN AUTH=LOGIN AUTH=OAUTHBEARER AUTH=XOAUTH2] Dovecot ready.
IMAP: 07:49:04 [tx] g8mz CAPABILITY
IMAP: 07:49:04 [db] OnNotify: asOld = 5, asNew = 5, ae = 3
IMAP: 07:49:04 [rx] * CAPABILITY IMAP4rev1 SASL-IR LOGIN-REFERRALS ID ENABLE IDLE LITERAL+ AUTH=PLAIN AUTH=LOGIN AUTH=OAUTHBEARER AUTH=XOAUTH2
IMAP: 07:49:04 [rx] g8mz OK Pre-login capabilities listed, post-login capabilities have more.
IMAP: 07:49:04 [tx] LOGIN command sent
IMAP: 07:49:04 [db] OnNotify: asOld = 5, asNew = 5, ae = 3
IMAP: 07:49:04 [rx] * CAPABILITY IMAP4rev1 SASL-IR LOGIN-REFERRALS ID ENABLE IDLE SORT SORT=DISPLAY THREAD=REFERENCES THREAD=REFS THREAD=ORDEREDSUBJECT MULTIAPPEND URL-PARTIAL CATENATE UNSELECT CHILDREN NAMESPACE UIDPLUS LIST-EXTENDED I18NLEVEL=1 CONDSTORE QRESYNC ESEARCH ESORT SEARCHRES WITHIN CONTEXT=SEARCH LIST-STATUS BINARY MOVE SNIPPET=FUZZY PREVIEW=FUZZY STATUS=SIZE SAVEDATE XDOVECOT LITERAL+ NOTIFY SPECIAL-USE QUOTA
IMAP: 07:49:04 [rx] 5ztu OK Logged in
IMAP: 07:49:04 [tx] b8hr IDLE
IMAP: 07:49:04 [db] Connection to 'imap.comcast.net' closed.
IMAP: 07:49:04 [db] OnNotify: asOld = 5, asNew = 0, ae = 5

During a bad time, the log indicated that Outlook received an IPV6 address ({2001: 558:fc18:1:f816:3eff:feee:56a7]) and the attempted connection timed-out (WSAGETSELECTERROR = 10060).

IMAP: 10:03:19 [db] Connecting to 'imap.comcast.net' on port 993.
IMAP: 10:03:19 [db] OnNotify: asOld = 0, asNew = 2, ae = 0
IMAP: 10:03:19 [db] srv_name = "imap.comcast.net" srv_addr = [2001:558:fc18:1:f816:3eff:feee:56a7]:993
IMAP: 10:03:19 [db] OnNotify: asOld = 2, asNew = 3, ae = 1
IMAP: 10:03:19 [db] OnNotify: asOld = 3, asNew = 4, ae = 0
IMAP: 10:03:40 [db] err: WSAGETSELECTEVENT = 0x10, WSAGETSELECTERROR = 10060
IMAP: 10:03:40 [db] Connection to 'imap.comcast.net' closed.

Outlook then repeated the attempt about 15 times and finally ended with this notice.

IMAP: 10:08:56 [db] ERROR: "The connection to the server failed.", hr=2148322318
IMAP: 10:08:56 [db] Connection to 'imap.comcast.net' closed.

A DNS query to my ISP’s IMAP farm indicates that it has dozens of server addresses, some in IPV4 and some in IPV6. I presume that it provides my workstation an address based on load-balancing, but I do not really know.

I have adjusted registry settings on my workstation to give preference to IPV4 addressing over IPV6 addressing, per the article at configure-ipv6-in-windows . I will see if this helps my Outlook startups behave more reliably. But this is not a long-term solution.

I wish to know if anyone in the forum is aware of any “official” pronouncements from Microsoft that would support my theory that Outlook has issues with IPV6 addresses for MAPI servers—and if so, what they suggest doing about it. If on the other hand, Microsoft’s position is that Outlook should work just as well with IPV6-addressed MAPI servers as it does with IPV4-addressed ones, then I will have to pursue this issue with my ISP—to see why my workstation cannot connect to their IPV6-addressed servers. Good luck with that, huh?

My Configuration:
Windows OS = Windows 10 Home, Version 20H2, Build 19042.746
Office = Microsoft 365 Subscription
Outlook = Microsoft 365 MSO (16.0.13628.20128) 32-bit
Windows Mail = Version 16005.13426.20566.0
ISP = Xfinity
Mail servers = mapi.comcast.net & smtp.comcast.net
Mail setup = email-client-programs-with-xfinity-email

Answer 1

Hi @Felix1058 ,

According to your description, the issue occurred when your Outlook connected to IPv6 address, considering you have tried to configure "Prefer IPv4 over IPv6" on your client, did your issue have any difference after that? If the issue is indeed related to IPv6, agree with Andy, maybe you could try to disable it to check.

I wish to know if anyone in the forum is aware of any “official” pronouncements from Microsoft that would support my theory that Outlook has issues with IPV6 addresses for MAPI servers

I have researched a lot about it but haven't found any related information, but for your issue itself, in the point of Outlook, we could also try to troubleshoot it via SaRA tools, which works by running tests to figure out what's wrong and offers the best solution for the identified problem, hope that would be helpful to you.

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Answer 2

I don't know, seems to me that disabling or preferring IPv4 is a good long term solution: https://learn.microsoft.com/en-us/outlook/troubleshoot/connectivity/outlook-shows-disconnected-if-ipv6-is-enabled

Just as an aside. You aren't using MAPI here :)

Answer 3

Thank you for your responses, anonymous userdavid and @Jade Liang-MSFT . The problem may have fixed itself. :-)

I recently found my ISP's test (test-ipv6.comcast.net ) for checking IPV4 and IPV6 connectivity from my workstation. It indicated success for the former and failure for the latter, which correlates with the behavior I was seeing in Outlook startups recently. As a shot in the dark, I power-cycled my Xfinity modem this morning and retried the test. This time, the test succeeded for IPV6 (as well as IPV4).

I theorize that something went amiss in the connection to my ISP a few weeks ago, causing me to lose IPV6 capability. That led to the intermittent timeout issues with Outlook startups. But by resetting my ISP connection, I have regained that capability.

So I will back off the registry setting for preferring IPV4 over IPV6 addresses for now. If my Outlook startups behave without timeouts over the next couple weeks, I will declare victory!