Vistaprint Email won't recognize user name at setup

Chris, Thanks very much for your reply. I have seen the article you referenced and went through it again to no avail. Here is another interesting nugget, Even though the account has been deleted from my Mac, I am still RECEIVING Emails on the account?? IF I go direct to the Vistaprint web client, I can see all my emails and log in no problem, same for my iPhone and iPad... sending and receiving is no problem on all other devices. Almost seems like this email account is "hiding" on my Mac and has bad information on it. The account does not show up in any of the traditional places (i.e. mail>preferences>accounts, etc.) Again, appreciate your help and insight!

Thanks for your input. I have had a lengthy support call with Vistaprint and all of the settings are correct. I also tried to enter all of the information as you suggested but same result. Does not recognize username or password.

That is what is baffeling about this. The exact same account information works on my other devices, so I know it is correct. Or, it would not work there. The fact that the mail account does not even exist on my Mac, yet is still receiving email from this account makes no sense to me. How can an unconfigured email account receive emails. Could there be some interplay with iCloud going on here?

My original thread.....Running a Macbook Pro with OS 10.11.6 and Mac Mail 9.3. Have had a Vistprint IMAP email account running fine on this forever. Suddenly in Early August it stopped sending emails from this account (didn't recognize password or user name). Neither was changed. Was still receiving email fine. Just can't send. Same account running fine on both iphone and iPad so I know info is correct. Tried deleting the account completley from Mac and now, when trying to "add a new account" it will not recognize the user name (email address) and password, which I know work on iphone and iPad. Almost like something in the Mac is preventing or blocking communication with Vistaprint server. Further to this, now that the account is deleted and does not exist in all the obvious places, I still receive email on this account!

They show up in the Apple Mail in box, just as they always did. Yet there is no account for that email that displays in my accounts screen (remember that I deleted that account as part of troubleshooting). So if an inbound email server is not configured somewher on my Mac, how are they getting to account.

I now know how the Vistaprint mail is getting to the Mac. It is being forwarded through another functioning email account. So that was unrelated to the main problem of not being able to configure and sign into Vistprint on the Mac. Vistprint is configured to send new Email to my Gmail account which I also access through Mac Mail.

Looked at all that but still can't setup Vistaprint Email on this Mac. It simply will not connect with the verified correct user name password, and servers. It is really strange. It worked for years without issue.

Checked connection doctor and its not there.