Outlook crashes as soon as you open it, any advice would be appreciated (applies to new and classic Outlook for Windows)

Question

Outlook crashes as soon as you open it, any advice would be appreciated (applies to new and classic Outlook for Windows)

Timothy Penny 5

Good morning,

We have been running outlook with Stack Mail accounts for a good few years now in our business. Never had any issues what so ever, but last week it crashed (went into "Not Responding" mode and never came back to life). Since then it crashes every time you start it if it starts at all. I tried "Quick Repair" and "Online Repair" features, the program opens after one of these, but as soon as you try to access one of the Stack Mail email accounts it freezes. So I thought the accounts were the issue, and I started removing them from Outlook but it had not had any effect. Right before typing this I did the Quick Repair and started Outlook, it started with no issues and it seemed like it was syncing up emails but as soon as I clicked the Help tab it has gone into Not Responding again. Does anyone have any ideas on how we could fix this?

Thank you in advance.

P.S We get the same issue in both the new and classic Outlook.

P.S.S The mobile we have set up with all the stack Mail accounts works perfectly fine with no issues at all.

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3 answers

Answer 1

Liora D 15,800 Microsoft External Staff Moderator

Dear @Timothy Penny,

Welcome to Microsoft Q&A.

Thank you for providing the details, I’m really sorry to hear how disruptive this has been.

Could I ask a few quick questions to help narrow down the cause?

Does Outlook freeze immediately on launch, or only after clicking certain tabs (like Help or File)?
Have there been any recent Windows or Office updates before the issue started last week?
Are there any COM Add‑ins enabled in your Classic Outlook? (Even one outdated add‑in can cause startup crashes.)

While waiting for your reply, here are a few steps that have helped other users facing the same symptoms:

Try starting Outlook in Safe Mode. This bypasses all add‑ins.

Press Window + R and type Outlook.exe /safe then click OK. If Outlook opens normally in Safe Mode, it points to an add‑in conflict.

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Create a new Outlook profile

If the profile is corrupted, Outlook often opens once after a repair and then breaks again — exactly as you described.

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Creating a new profile can help confirm this.

Re‑create the local Forms library folder

Recently, several users reported crashes caused by missing or corrupted Forms Library.

You can try this workaround:

Close Outlook, Open File Explorer > paste: %localappdata%\Microsoft. Create a new folder called FORMS2 then Restart Outlook

Check for pending Windows or Office updates

Some recent updates have caused crash loops, and fixes were released shortly after.

These steps won’t require removing your email accounts again and often help isolate the root cause quickly.

Please understand that our initial response does not always resolve the issue immediately. However, with your help and more detailed information, we can work together to find a solution.

Please feel free to reply with the answers to the questions above, I’d be more than happy to help you work through the issue step by step. You’ve already done a lot of the right troubleshooting, so we’re definitely close to identifying the exact cause.

Looking forward to hearing back from you with any updates or additional details.

Warm regards,

If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".

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Timothy Penny 5 Reputation points

2026-01-19T11:32:35.9633333+00:00

Hello,

Thank for your reply.

I have created a new profile for Outlook and it stopped the crashes. Outlook seems to be running fine now. I am trying to add our Stack Mail accounts to it now. I have added Sales account with no issues, But the other two accounts returning this message:

Passwords are correct. Would this be an issue on their end?
Liora D 15,800 Reputation points Microsoft External Staff Moderator

2026-01-19T13:53:43.3166667+00:00
Hi @Timothy Penny,

I’m really glad to hear that creating a new Outlook profile has stopped the crashes, that’s great progress.

Regarding the new problem you’re seeing when adding the remaining two Stack Mail accounts:

The message “We couldn’t log on to the incoming (IMAP) server” indicates that Outlook is unable to authenticate with the IMAP server, even though the password may be correct.

Since your Sales account was added successfully, Outlook and the new profile are working normally so this part is not related to the previous crash.

When only specific IMAP accounts fail while others work, it’s often due to something on the mailbox provider’s side or differences in the individual account settings.

To help narrow this down, could you please check the following:

Can you sign in to those two accounts using Stack Mail’s webmail interface? (For example: https://webmail.stackmail.com)

Are IMAP and SMTP definitely enabled for those mailboxes? Some providers allow per‑mailbox toggles.

Are all three accounts using the exact same IMAP settings?

For example:

IMAP server: imap.stackmail.com

Port: 993

SSL/TLS: On

Have those two accounts ever required an app‑password or had security settings changed recently?

Even a small difference between the accounts (quota, security settings, or a temporary block on the provider’s side) can cause exactly the error message you’re seeing.

Once you’re able to confirm the points above, I’ll be happy to help you continue from there.

Looking forward to your update.
Timothy Penny 5 Reputation points

2026-01-20T09:01:23.0166667+00:00

Yes we can sign in on stackmail webmail interface as usual.

IMAP / SMTP settings are enables on all stackmail accounts & using the same settings.

No accounts have had any settings changed or required a sperate app password.
Liora D 15,800 Reputation points Microsoft External Staff Moderator

2026-01-20T15:46:00.3133333+00:00

Hi @Timothy Penny,

Thanks for the quick update, that helps narrow things down. Since you can sign in to Stack Mail webmail as usual, IMAP/SMTP are enabled, all accounts use the same settings, and no app passwords are required, the pattern strongly suggests a per‑mailbox condition on the provider side of IMAP rather than an Outlook/client defect. In other words, your new Outlook profile is healthy (proven by the Sales mailbox working), but those two specific mailboxes are being treated differently by the IMAP service.

In practice, we see this when a mailbox hits a server‑side threshold (temporary lock/throttle after prior failures), sits on a different backend node with a stale auth cache, is near quota, or has a subtle security flag that blocks IMAP while webmail continues to work (webmail authenticates through a different path than IMAP). It can also be as small as a hostname/certificate mismatch that only affects certain mailboxes when the provider runs multiple IMAP endpoints.

If you have access to the provider panel, change the password on those two mailboxes (just once, to refresh the IMAP auth state), then add them in Outlook using Advanced setup > IMAP with the same canonical hosts/ports as your working Sales account. If the same error persists immediately after a known‑good password reset, involve Stack Mail support and ask them to check IMAP authentication logs for those two addresses at your test time. The key things to ask them to confirm are any temporary blocks or throttling on your public IP, per‑mailbox security flags/app‑password requirements that might have been enabled recently, quota state, and whether those two mailboxes live on a different server/node than the Sales mailbox.

If you can try one neutral client (e.g., Thunderbird, Windows Mail..) on the same PC, using the identical IMAP settings that work for Sales, and it fails for the same two mailboxes, that’s strong evidence the issue is provider‑side and gives their support team a clear signal to look at the server logs rather than Outlook.
Liora D 15,800 Reputation points Microsoft External Staff Moderator

2026-01-21T14:35:56.7933333+00:00

Hi Timothy Penny,

I just wanted to follow up to see how things are going with the information I shared above. I truly hope it was helpful and brought you closer to resolving the issue.

If you’ve had a chance to review it and have any updates, questions, or if you ran into any difficulties along the way, please don’t hesitate to let me know. I’m more than happy to assist further if needed.

It would be great to hear back from you!

Warm regards,

Liora.
Liora D 15,800 Reputation points Microsoft External Staff Moderator

2026-01-25T14:38:51.67+00:00

Hi @Timothy Penny,

Just checking in one last time to see if you still need any assistance with this topic. I completely understand that things can get busy, so no worries at all if you haven’t had a chance to respond yet.

If the information shared earlier helped resolve your issue, feel free to click "Accept Answer" to help others with similar questions. Otherwise, I’m still here and happy to support you whenever you're ready.

If you have any other questions in the future, please don’t hesitate to create a new thread, other moderators and I are always happy to help. We truly hope you have a smooth experience with Microsoft products and wish you continued success in your work.

Best regards,

Liora.

Answer 2

Abdelrahman Mohamed 0

I have a problem with Outlook; it closes automatically as soon as I open it.

Stefan Blom 341.4K Reputation points MVP Volunteer Moderator

2026-03-21T22:35:44.26+00:00

I have a problem with Outlook; it closes automatically as soon as I open it.

For troubleshooting, see https://www.slipstick.com/outlook/basic-troubleshooting-steps-for-outlook/ .

If you need further assistance from your peers in the forum, consider starting your own thread. Use the Ask a question button at the top of the page. Good luck.

Answer 3

It sounds like you're experiencing a frustrating issue with Outlook crashing. Here are some steps you can take to troubleshoot and potentially resolve the problem:

Start Outlook in Safe Mode: This can help determine if the issue is caused by add-ins. To do this, press Windows + R, type Outlook /safe, and press Enter. If Outlook works in Safe Mode, consider disabling add-ins one by one to identify the culprit.
Repair Office: Since you've already tried Quick Repair and Online Repair, ensure that you follow the steps correctly. Sometimes, running the repair multiple times can yield different results.
Create a New Outlook Profile: Corrupted profiles can cause crashes. To create a new profile, go to Control Panel > Mail > Show Profiles > Add. Set up your email accounts in the new profile and see if the issue persists.
Check for Conflicting Software: Sometimes, other software can interfere with Outlook. Consider performing a Selective Startup to identify if any background applications are causing the issue. You can do this by using the System Configuration tool (msconfig).
Update Outlook and Windows: Ensure that both Outlook and your Windows operating system are fully updated. Missing updates can lead to compatibility issues.
Disable Antivirus Integration: If your antivirus software integrates with Outlook, it may cause performance issues. Try disabling this integration or temporarily disabling the antivirus to see if it resolves the problem.
Run Outlook Diagnostics: Use the Microsoft Support and Recovery Assistant to run diagnostics on Outlook. This tool can help identify and fix various issues.

If the problem continues after trying these steps, you may want to consider reaching out to Microsoft Support for further assistance.

References:

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Outlook crashes as soon as you open it, any advice would be appreciated (applies to new and classic Outlook for Windows)

3 answers