Cannot create a mailbox: SOAP failed. No additional info

Symptoms

• The following error is shown in Plesk UI when creating a mailbox:

  PLESK_ERROR: SOAP failed. No additional info

• Following entries in %plesk_dir%admin\logs\php_error.log:

  CONFIG_TEXT: ERR [panel] mailmng failed: SOAP failed. No additional info
  at (SmarterMail::checkResult line 185)
  at Get maxLetterSize via svcServerAdmin Web Service(SmarterMail::SMProvider::maxLetterSize line 431)
  at execute console command --get-max-letter-size(vconsoleapp::start line 100)
  at execute "C:\Program Files (x86)\Parallels\Plesk\admin\bin\mailmng.exe" --get-max-letter-size(vconsoleapp::run line 117)

• The same error is shown in Event Viewer > Applications ans Services Logs.

• Error when accessing Mail Server Settings in Tools & Settings:

  PLESK_INFO: Operation Failed
  The operation you were performing failed. You can retry the operation with our without changing its parameters.
  

• Mail sending/receiving doesn't work.

• SmarterMail is used as a mail server.

Cause

SmarterMail essential services are stopped.

Resolution

1. Connect to the server via RDP.

2. Open Start menu > Services and start SmarterMail Service and SmarterMail Web Server services: