SMTP error

using an external smtp server (my host doesn't want me using smtp on me VPS, but I can do so as a last resort) I have configured my smtp server settings as you'd expect it to be configured - email host confirmed this. I run smtp test php and I get: ----Resolving SMTP server domain "mail.privateemail.com"...Connecting to host address "[redacted IP address]" port 110...S +OK Dovecot ready.C USER jimmi@*x.comS +OKC PASS .S +OK Logged in.Resolving SMTP server domain "mail.privateemail.com"...Connecting to host address "[redacted IP address]" port 26...Connected to SMTP server "mail.privateemail.com".S 220 PrivateEmail.com Mail NodeC EHLO mail.privateemail.comS 250-mta4.ox.privateemail.comS 250-PIPELININGS 250-SIZE 81788928S 250-ETRNS 250-STARTTLSS 250-AUTH PLAIN LOGINS 250-ENHANCEDSTATUSCODESS 250-8BITMIMES 250 DSNC MAIL FROM:<>C RCPT TO:<j>C DATAS 250 2.1.0 OkS 553 5.7.1 <jimmi@m.com>: Sender address rejected: not logged inDisconnected.Could not send the message to **@**co.uk. Error: 553 5.7.1 : Sender address rejected: not logged in----Now I have a strong feeling its because the host requires sasl 'login' type authentication... when I set require sasl.php in the test mail php page in browser I get a 500 error. This suggests sasl not working / configured properly, right? I have a few mission-critical errors with the script and would be willing to pay (although I have little budget) for someone to help me make it work...