hmmm...

• ACL entry
• possible login credentials
• send only to gmail.com emails (ie you can't use gmail.com to "proxy" emails to non gmail accounts without logging in first)
• The "from" address matches the address you used to login (if you are logging in)
• if not "gmail.com", the domain in the "from" address has a DNS entry.
• This value may need to match a reverse DNS lookup.
• The mail server's HELO needs to be legit
• The mail server may need to be using EHLO instead
• your server is not on any of the DNS-blacklists
• emails aren't heuristically classified as SPAM
• etc.

You don't need all of them (except ACL entry -- start there)

It really is all about your email infrastructure.

... and proving to the remote server that you aren't a spammer.

MK

Also important: what is your Apex version? Check the documentation for your specific version. E.g. for 5.1:

APEX_MAIL.PUSH_QUEUE( p_smtp_hostname             IN    VARCHAR2 DEFAULT NULL, p_smtp_portno               IN    NUMBER   DEFAULT NULL); 

Note that these parameter values are provided for backward compatibility, but their respective values are ignored. The SMTP gateway hostname and SMTP gateway port number are exclusively derived from values entered on the Manage Environment Settings when sending email.

So, your parameters ('smtp.gmail.com',465) are ignored. You have to setup your smtp connection via your workspace.

1. Go through Mike's list.

2. Check the Apex mail queue for errors.

Were you successful in sending email via GMAIL. ? DID MIke's list help?