Hello, I don't know what is happened with Qmail and SMTP server in Plesk panel. But when i try send any emails through any domains on server i get again again request for password for SMTP (any email account on server) and when i put correct password outlook ask me again about password. I've tried send email through telnet with SMTP commands and i get error, look: telnet mail.mydomain.com 25 Trying 200.XX.XXX.XX... Connected to mail.mydomain.com (200.XX.XXX.XX). Escape character is '^]'. 220 www.mydomain.com ESMTP EHLO www.mydomain.com 250-www.mydomain.com 250-AUTH=LOGIN CRAM-MD5 PLAIN 250-AUTH LOGIN CRAM-MD5 PLAIN 250-STARTTLS 250-PIPELINING 250 8BITMIME AUTH LOGIN 334 VXNlcm5hbWU6 pop account base64 coded 334 UGFzc3dvcmQ6 email pass base64 coded unable to open mail authentication database: Invalid argument 535 auth failure End everytime this error: "unable to open mail authentication database: Invalid argument" I've tried everything for fix it and nothing. Please help to me!