VerifySmtpLogin reports success with any login/password?

If your SMTP server does not require authentication, then VerifySmtpLogin will always return true because there is no login/password to verify. If you examine the mailman.LastErrorText after calling VerifySmtpLogin, you can spot it by the presence of this line:
login_method: NONE or already authenticated

Also, this line will be missing in the hello response:
250-AUTH LOGIN PLAIN

For example, here are two LastErrorText samples — one uses chilkatsoft.com’s mail server, which requires authentication. The other uses sbcglobal.net’s server, which does not. (The reason sbcglobal.net requires no authentication is that authentication was required initially to log onto the network (via DSL). The only people that can physically connect to sbcglobal.net’s SMTP server are those that have already authenticated — so no additional authentication is required.) The LastErrorText for the sbcglobal.net does not include the original IP addresses or usernames.

sbcglobal.net LastErrorText — No authentication required:

ChilkatLog:
  VerifySmtpLogin:
    DllDate: Oct  1 2007
    Username: JohnDoe
    Component: ActiveX
    SMTP_Connect:
      Connecting to SMTP server smtp.sbcglobal.net:25
      smtp_host: smtp.sbcglobal.net
      smtp_port: 25
      smtp_user: johnDoe@sbcglobal.net
      InitialResponse: 220 flpi102.prodigy.net ESMTP Sendmail 8.13.8 out.dk.spool/8.13.8; Tue, 13 Nov 2007 17:20:07 -0800
	
      sendingHello: EHLO LAPTOP
	
      helloResponse: 250-flpi102.prodigy.net Hello adsl-89-188-99-249.dsl.irvnca.pacbell.net [89.188.99.249], pleased to meet you
250-ENHANCEDSTATUSCODES
250-PIPELINING
250-8BITMIME
250-SIZE 10240000
250-DSN
250-DELIVERBY
250 HELP
	
      <strong>login_method: NONE or already authenticated</strong>
      CONNECTED to ESMTP server smtp.sbcglobal.net:25

chilkatsoft.com LastErrorText — Requires authentication:

ChilkatLog:
  VerifySmtpLogin:
    DllDate: Nov  7 2007
    Username: Chilkat
    Component: Ruby
    SMTP_Connect:
      Connecting to SMTP server mail.chilkatsoft.com:25
      smtp_host: mail.chilkatsoft.com
      smtp_port: 25
      smtp_user: admin@chilkatsoft.com
      InitialResponse: 220 mail.chilkatsoft.com ESMTP  648143d3667b3045487bb901cdbbf649
	
      sendingHello: EHLO CK2007
	
      helloResponse: 250-mail.chilkatsoft.com
250-PIPELINING
250-SIZE 100000000
250-DATAZ
<strong>250-AUTH LOGIN PLAIN</strong>
250 8BITMIME
	
      login_method: LOGIN
      CONNECTED to ESMTP server mail.chilkatsoft.com:25