Outlook will not open! I've tried at least 6 times and can't open it after i closed it down. i need to access my mail. i use Win 10 Pro

Hi, I'm Diane and will be happy to help you today. >> in any event, i need to be able to know how to get Outlook to open! << It not opening because you didn't enter the password or is there another error message? Are all 3 mailboxes at yahoo? The newest builds of Outlook support oAuth2 for yahoo accounts, so you no longer need to create an app password. The dialog is standard when using oAuth2. Outlook only sees the email address - and of course, it needs to access email and attachments to sync them. If you have any questions, don't hesitate to ask. -- Diane Give back to the community. Help the next person with this problem by indicating whether this answer solved your problem. Click Yes or No at the bottom.

Hello Diane, Thank you for your reply. Outlook was able to open after I re-started my computer this morning. All 3 of my email addresses were originated in Yahoo 17 years ago. They are also used in Outlook. My servers have the correct port numbers (993 and 465). I don't understand why Yahoo went from using a secure mail key for each of my three email addresses to this new way of accessing my Outlook mail. I'm from the old school of NOT fixing something that isn't broke! Anyway, a couple of questions - if i uninstall Outlook and then re-install it, will i lose any of my messages and/or folders? Will using the password from this new 'sign in' method using just one of my email addresses open all three of my Outlook addresses?

I just noticed something that really has me concerned. One of my addresses has it's folder filled with another addresses mail. Says there is an ox800ccc78 error. I'm afraid to attempt to do anything about it for fear of something happening to my other addresses that seem to be working ok. Why would mail from one address wind up in another addresses folder?

>> I'm from the old school of NOT fixing something that isn't broke! << So am I, but it was broke. The app password generator at yahoo didnt work half the time for half for many users, possibly because they wanted people to use oAuth2 - which Microsoft finally added to Outlook. >> Will using the password from this new 'sign in' method using just one of my email addresses open all three of my Outlook addresses? << If they are different yahoo accounts, no. If it's one yahoo account and you get mail to all 3 addresses in the inbox, yes. >> Says there is an 0x800ccc78 error. << That is an authentication error - you have the wrong username and password or outgoing settings. What is the complete send and receive error message? Depending on the complete error message, this might explain it: https://support.microsoft.com/office/i-receive-a-550-553-or-relay-prohibited-error-when-sending-email-messages-65b494a4-0a15-433e-829f-e73651e0245e

Good morning Diane,

Sorry for getting back to you late but I was never notified that you had replied. The reason for that is because that email address DD45 isn’t working in Outlook. I only noticed it because I checked the website. Until DD45 address gets fixed, you’ll have to reply to *** Email address is removed for privacy ***. I have three Yahoo email addresses (DD358, DD45 and DS). DD358 I use 99% of the time. Each one has it’s own password. The same thing was required for the secure mail key that they initiated a while ago. Currently, DD358 and DS are working in Outlook as they should. DD45 is the one giving me a problem. As I had mentioned, messages for DD358 are now in the DD45 folder. That happened AFTER I tried to sign into my mail on Outlook! How did mail from one address get transferred to a different one (DD45 to DD358) and how do I correct that?? Most importantly, my question about that address was “do I use the same Yahoo DD358 password to access my messages for ALL addresses in Outlook”? I do understand that I have to check the port for IMAP and SMTP and make a correction if necessary but don’t want to attempt to do it until I hear back from you on the above questions. The 0x800CCC78 error message is “cannot send the message, verify the email address in your account properties. The server responded: 550 request failed; Mailbox unavailable”.

Thank you.

Update: I went ahead and tried to sign in to DD45 after checking to make sure the server settings were correct and could NOT sign in to Outlook for this address. The server settings are exactly the same for all three addresses. I used the same Yahoo password that I did before to ‘fix’ the other two addresses. For some reason, this address (DD45) won’t accept that password. In addition, as mentioned previously, ALL the DD358 messages are in the DD45 folder and NO new DD45 messages appear in the folder! I have absolutely no idea how messages from one address got into another address folder. Any ideas?

Update: I went ahead and tried to sign in to DD45 after checking to make sure the server settings were correct and could NOT sign in to Outlook for this address. The server settings are exactly the same for all three addresses. I used the same Yahoo password that I did before to ‘fix’ the other two addresses. For some reason, this address (DD45) won’t accept that password. In addition, as mentioned previously, ALL the DD358 messages are in the DD45 folder and NO new DD45 messages appear in the folder! I have absolutely no idea how messages from one address got into another address folder. Any ideas?

>> How did mail from one address get transferred to a different one (DD45 to DD358) and how do I correct that?? << If you only add DD358 to Outlook, is mail from DD45 in the mailbox? (Or log into the account at yahoo.com) Do you have the account forwarding or connected to the other account? >> do I use the same Yahoo DD358 password to access my messages for ALL addresses in Outlook”? << If they are totally separate mailboxes, you need to use the correct password for each account. And you may need to get an app password for the account if Outlook doesn't bring up the oAuth2 dialog.

I'm not that much up on all the terminology used. Please explain what oAuth2 dialog is. Is that the Yahoo login questions?

To recap, I have three different email addresses (DD358, DD45 and DS). The only one not working in Outlook is DD45. The other two are working as they are supposed to. I changed the password for DD45 in Yahoo but still can't access the mail in Outlook. AND - all my DD358 incoming mail is still in the DD45 folder! There are NO DD45 messages in it's folder! I logged into the DD45 folder with Yahoo and all the DD45 messages were there (no DD358 messages were in the DD45 folder). I don't understand what you mean by "Do you have the account forwarding or connected to the other account?". The DD45 account is all by itself. No other account is connected to it. whenever i try to open DD45 in Outlook, i get this message: "incorrect user ID or password. care code: 201 [LU100].

This is extremely frustrating... One last question, does the Secure Mail Key(s) that were used before have anything to do with Outlook being able to access the Yahoo server or is it now something that doesn't even matter? Thank you for all your help.

Remove DD358 from your profile - this should leave one yahoo account (since DD45 isn't working) - then restart Outlook. Add DD358 back - are you still getting DD45's mail in that account? >> Please explain what oAuth2 dialog is. Is that the Yahoo login questions? << It's the yahoo sign in page - not Outlook's normal password dialog (which requires an app password) - in my case, I need to tap yes on the yahoo weather app on my phone then enter a 4 character code. When i'm done, I get this dialog: Microsoft's article on this: https://support.microsoft.com/office/how-to-add-a-yahoo-imap-account-to-outlook-desktop-without-an-app-password-d13fb02d-eb93-4775-bae9-0e54bf2f5bca If you do not get the yahoo signin dialog like you get when signing in on a browser, you need to use an app password. >> One last question, does the Secure Mail Key(s) that were used before have anything to do with Outlook being able to access the Yahoo server or is it now something that doesn't even matter << If you get the dialog that asks for other proofs.

Thanks for getting back to me. For someone like me that isn't very computer literate, this is extremely confusing and exasperating! I had to leave my desk for a couple hours and when I returned there was a popup that asked me to sign into DD45. Before i could do so, another popup said "welcome". Somehow, DD45 fixed itself! then another bomb exploded! While checking out DD45, Yahoo asked me to sign into DS. Said i used the wrong password. tried two of them. used the DS password and it didn't work and the DD358 one worked. However, now ALL the DD358 mail is in the DS folder which is just the same problem i had with DD45 (mail in wrong folder). further, a popup said i had a IMAP server error. so, one fixes itself and the other becomes a problem! Oh boy!! Right now i'm afraid to remove DD358 from Outlook and the add it back. it's the main one i use and can't afford to screw it up! while you are reading this message, i'll be trying to fix the IMAP for DS. thank you