Still not working almost 1 week now. 
Even I have tried account deletion (both in em Client and in outlook.com) and re-addition. Still no luck!
Seems like an issue with your account. Might be best for you to contact your email provider and ask for assistance.
It is working fine with other email clients. So it cannot be an account issue.
Yet the error is coming from your email provider. Have you contacted them?
This error message is from the eM Client not from the service provider. Yes, I agree that this error message from the eM Client could come from some SMTP error from the service provider. But in that case the SMTP error from the service provider will be useful.
Hi,
I have the same problem. Unable to send from emclient with smtp-mail.outlook.com.
What I tried:
Deleted outlook account from emclient.
Uninstalled emclient
Removed emclient access to the account from outlook.com
Reinstalled emclient
Reinstalled Outlook email account in eMclient
Outgoing email still stuck in the outbox
Tried to send from thunderbird ok
Tried to send with outlook.com ok
eMclient still unable to send
[SMTP] MailClient.Accounts.AuthenticationAbortedException: in the log file
Thank you 
HI. This sounds like a related problem that I’m having with eMC connecting to Outlook.com that returns an error message. Basically, won’t connect and sits there. The red triangle shown next to my email account. This has been ongoing for 8 days now. See my post from yesterday. “Getting error…”
It is working now. I did not do anything else now.
It may be an issue with your specific account. Did you contact your email provider for assistance?
Just resolved itself for me too, not as a result of anything I did. As suddenly and inexplicably as it first stopped sending n(still receiving), EMC now sends and receives.
I’m having this problem now as well. Made no changes to account, same settings as shown in this thread. Turned off antivirus.
Hi,
I have the same problem with all my Outlook accounts on my laptop since yesterday - I can receive but not send emails.
[SMTP] MailClient.Accounts.AuthenticationAbortedException: in the log file.
I’ve tried literally everything except reinstalling the program. I have EMC 8.2 installed. It can’t be a problem with those specific accounts because I can send emails from the same accounts on another (old computer) where I have the EMC 7.2 installed, without any problem!
Thanks in advance.
Thank you for your prompt response 
. I will try the suggested solution and hopefully the workaround is helpful.
I can confirm that setting up the account with an older version of the OAuth authentication works so far. Thanks!
@Gary Could you please pin or highlight the suggested solution so far? And also point clearly that this is not a problem with specific account or account providers but an issue with the program that is being addressed (?).
Thanks…
Could you please pin or highlight the suggested solution so far?
The temporary solution for the Microsoft sending mail issue causing the error “[SMTP] MailClient.Accounts.AuthenticationAbortedException: Authentication aborted” if you have an eg: Outlook.com, Hotmail.com or Live.com or similiar MS acct is in the eM Client support page link below which is also (at the bottom) of the link above that @Gary already advised.
And also point clearly that this is not a problem with specific account or account providers but an issue with the program that is being addressed (?).
This specific issue is with Microsoft and not eM Client as per the eM Client support pages advise.
Hi, @cyberzork .
Well, eM Client Support page can the issue is with the NASA or an alien attack, if they want. But the truth is that no other email client I use has been affected (Windows, MacOs, Android, iOS).
Not to mention is taking for ever to release a serious fix. So… from the customer perspective I have, this is a problem with eM Client, in all platforms.
When will a version with a fix be released?
(Maybe they can try hiring more o better developers instead of so many moderatos that provides misleading information)
Thunderbird have now also released a fix for this. But some apps may not be affected because they use an older form of oAuth. That is where the issue arises as your provider documented that they use modern oAuth, and they did until recently, but then they broke their implementation.
Unfortunately the issue is not with eM Client otherwise we would have already fixed it. But we did release a workaround so you can continue to send until your email provider can fix it.
Tried this fix and it worked but now it’s back to the same issue of not being able to send mail. I have tried adding and removing the patch and neither works. I can receive mail fine but not send anything.