Plesk is set up to use SmarterMail as mail server.
While creating or updating email address. the following error is reported:
Internal error: Can't open domain. Domain: domain.tld [domain.tld]. Reason: You have already attempted to log in too many times within a short period. You must wait a set amount of time before trying again. If you require assistance, please contact your email administrator. (Error code 1) File Agent.php Line 212 Type PleskUtilException
Integration of Plesk with SmarterMail is broken.
Go to Tools & Settings > Server Components > Mail Server and submit working SmarterMail administrator credentials.
Add SmarterMail site in IIS as suggested in this article.
Register SmarterMail as the default mail server by executing below commands:
C:\>%plesk_bin%\defpackagemng.exe --get --force C:\>%plesk_bin%\defpackagemng.exe --update --type=mailserver --package=smartermail