ERROR: SMTP server rejected quit command:

FYI:
Drupal 6.4
PHP 5.2.6
Apache 2.2.8
Localhost

Using the SMTP module, I've sent and received the 'Test' email and similarly the new user 'Account Details' logon email.

However I note the following error reported after submitting 'Create New Account':

SMTP -> get_lines(): $data was "" SMTP -> get_lines(): $str is "220 mx.google.com ESMTP 20sm23513008wfi.11 " SMTP -> get_lines(): $data is "220 mx.google.com ESMTP 20sm23513008wfi.11 " SMTP -> FROM SERVER: 220 mx.google.com ESMTP 20sm23513008wfi.11 SMTP -> get_lines(): $data was "" SMTP -> get_lines(): $str is "250-mx.google.com at your service, [202.179.97.122] " SMTP -> get_lines(): $data is "250-mx.google.com at your service, [202.179.97.122] " SMTP -> get_lines(): $data was "250-mx.google.com at your service, [202.179.97.122] " SMTP -> get_lines(): $str is "250-SIZE 35651584 " SMTP -> get_lines(): $data is "250-mx.google.com at your service, [202.179.97.122] 250-SIZE 35651584 " SMTP -> get_lines(): $data was "250-mx.google.com at your service, [202.179.97.122] 250-SIZE 35651584 " SMTP -> get_lines(): $str is "250-8BITMIME " SMTP -> get_lines(): $data is "250-mx.google.com at your service, [202.179.97.122] 250-SIZE 35651584 250-8BITMIME " SMTP -> get_lines(): $data was "250-mx.google.com at your service, [202.179.97.122] 250-SIZE 35651584 250-8BITMIME " SMTP -> get_lines(): $str is "250-STARTTLS " SMTP -> get_lines(): $data is "250-mx.google.com at your service, [202.179.97.122] 250-SIZE 35651584 250-8BITMIME 250-STARTTLS " SMTP -> get_lines(): $data was "250-mx.google.com at your service, [202.179.97.122] 250-SIZE 35651584 250-8BITMIME 250-STARTTLS " SMTP -> get_lines(): $str is "250 ENHANCEDSTATUSCODES " SMTP -> get_lines(): $data is "250-mx.google.com at your service, [202.179.97.122] 250-SIZE 35651584 250-8BITMIME 250-STARTTLS 250 ENHANCEDSTATUSCODES " SMTP -> FROM SERVER: 250-mx.google.com at your service, [202.179.97.122] 250-SIZE 35651584 250-8BITMIME 250-STARTTLS 250 ENHANCEDSTATUSCODES SMTP -> get_lines(): $data was "" SMTP -> get_lines(): $str is "220 2.0.0 Ready to start TLS " SMTP -> get_lines(): $data is "220 2.0.0 Ready to start TLS " SMTP -> FROM SERVER: 220 2.0.0 Ready to start TLS SMTP -> get_lines(): $data was "" SMTP -> get_lines(): $str is "250-mx.google.com at your service, [202.179.97.122] " SMTP -> get_lines(): $data is "250-mx.google.com at your service, [202.179.97.122] " SMTP -> get_lines(): $data was "250-mx.google.com at your service, [202.179.97.122] " SMTP -> get_lines(): $str is "250-SIZE 35651584 " SMTP -> get_lines(): $data is "250-mx.google.com at your service, [202.179.97.122] 250-SIZE 35651584 " SMTP -> get_lines(): $data was "250-mx.google.com at your service, [202.179.97.122] 250-SIZE 35651584 " SMTP -> get_lines(): $str is "250-8BITMIME " SMTP -> get_lines(): $data is "250-mx.google.com at your service, [202.179.97.122] 250-SIZE 35651584 250-8BITMIME " SMTP -> get_lines(): $data was "250-mx.google.com at your service, [202.179.97.122] 250-SIZE 35651584 250-8BITMIME " SMTP -> get_lines(): $str is "250-AUTH LOGIN PLAIN " SMTP -> get_lines(): $data is "250-mx.google.com at your service, [202.179.97.122] 250-SIZE 35651584 250-8BITMIME 250-AUTH LOGIN PLAIN " SMTP -> get_lines(): $data was "250-mx.google.com at your service, [202.179.97.122] 250-SIZE 35651584 250-8BITMIME 250-AUTH LOGIN PLAIN " SMTP -> get_lines(): $str is "250 ENHANCEDSTATUSCODES " SMTP -> get_lines(): $data is "250-mx.google.com at your service, [202.179.97.122] 250-SIZE 35651584 250-8BITMIME 250-AUTH LOGIN PLAIN 250 ENHANCEDSTATUSCODES " SMTP -> FROM SERVER: 250-mx.google.com at your service, [202.179.97.122] 250-SIZE 35651584 250-8BITMIME 250-AUTH LOGIN PLAIN 250 ENHANCEDSTATUSCODES SMTP -> get_lines(): $data was "" SMTP -> get_lines(): $str is "334 VXNlcm5hbWU6 " SMTP -> get_lines(): $data is "334 VXNlcm5hbWU6 " SMTP -> get_lines(): $data was "" SMTP -> get_lines(): $str is "334 UGFzc3dvcmQ6 " SMTP -> get_lines(): $data is "334 UGFzc3dvcmQ6 " SMTP -> get_lines(): $data was "" SMTP -> get_lines(): $str is "235 2.7.0 Accepted " SMTP -> get_lines(): $data is "235 2.7.0 Accepted " SMTP -> get_lines(): $data was "" SMTP -> get_lines(): $str is "250 2.1.0 OK 20sm23513008wfi.11 " SMTP -> get_lines(): $data is "250 2.1.0 OK 20sm23513008wfi.11 " SMTP -> FROM SERVER: 250 2.1.0 OK 20sm23513008wfi.11 SMTP -> get_lines(): $data was "" SMTP -> get_lines(): $str is "250 2.1.5 OK 20sm23513008wfi.11 " SMTP -> get_lines(): $data is "250 2.1.5 OK 20sm23513008wfi.11 " SMTP -> FROM SERVER: 250 2.1.5 OK 20sm23513008wfi.11 SMTP -> get_lines(): $data was "" SMTP -> get_lines(): $str is "354 Go ahead 20sm23513008wfi.11 " SMTP -> get_lines(): $data is "354 Go ahead 20sm23513008wfi.11 " SMTP -> FROM SERVER: 354 Go ahead 20sm23513008wfi.11 SMTP -> get_lines(): $data was "" SMTP -> get_lines(): $str is "250 2.0.0 OK 1223526492 20sm23513008wfi.11 " SMTP -> get_lines(): $data is "250 2.0.0 OK 1223526492 20sm23513008wfi.11 " SMTP -> FROM SERVER: 250 2.0.0 OK 1223526492 20sm23513008wfi.11 SMTP -> FROM SERVER: SMTP -> ERROR: SMTP server rejected quit command:

I've checked Outstanding Issues and have not found a similar problem.

Regards,
Paul Boscher