SMTP error - sender thread limit exceeded

[mtorman]

Hello Support, we are a small company but we rely on your software daily, it is a solid performer.

Recently in the *server* logs I am noticing the following error after the OnFileUploaded (HTTP) event is triggered multiple times within a short time frame (like 4 times within 1 minute), due to multiple uploads by the same user:

"[05] Sun, 10 Jan 2021 12:46:07 Mail to upload_events@xxxxxx.com" rel="nofollow failed, send end to server error. : 432 4.3.2 STOREDRV.ClientSubmit; sender thread limit exceeded. Visit aka.ms/concurrent_sending for more info. [Hostname=xxxxxx.namprd19.prod.outlook.com]"

The aka.ms link resolves to an article about Microsoft changing their policies on how many *concurrent* SMTP connection threads can be established for sending emails - Apparently they are now limiting this to 3:

https://docs.microsoft.com/en-us/exchan ... provements" rel="nofollow

Is there any configuration setting to restrict how many instances of a particular event/script are allowed to execute simultaneously? Or any kind of rate-limiting feature that could be added? I've been googling this and searching your support resources/forums without success.

And I can't tell if the same email upload event notification is re-tried or if the script just stops for that instance/thread? Does it re-try sending the email, or just log the error and give up?

We are using Wing FTP v.6.3.7 (Corporate) and Office 365 (Exchange Online) email account. I understand this isn't the latest version but I didn't see any fixes for this specific issue on the release notes history page.

Appreciate your help, thanks.

[FTP]

If you mean the thread number in WingFTP, maybe you can set the working threads into "2" under "Server > Settings > General Settings > Miscellaneous > Working threads number".