[If it was possible to offer a Bounty, I would offer 200 points for this one.]

How do I successfully attach a file when sending an email via gmail in version 12.0.1.3298?

First, here are the results of my tests...

=====
Test 1: Message sent to @recipient = bcarter@bcarter.com and received OK, but 
the attachment is garbled in Microsoft Outlook...

test subject at 2011-04-05 14:11:57.148
Foxhound <breck.carter@gmail.com>
Tue 4/5/2011 2:12 PM
bcarter@bcarter.com
attachment.txt (140 B)
Thi
‡X-́¤`·u

=====
Test 2: Message sent to @recipient = Breck.Carter@gmail.com and received OK, but 
Google Mail refuses to display attachment...

from    Foxhound <breck.carter@gmail.com>
to  Breck.Carter@gmail.com
date    Tue, Apr 5, 2011 at 2:15 PM
subject test subject at 2011-04-05 14:15:50.824
mailed-by   gmail.com
    Important mainly because it was sent directly to you.
hide details 2:15 PM (0 minutes ago) 
test message at 2011-04-05 14:15:50.824
Oops... the virus scanner has a problem right now. Download at your own risk, or try again later.
    attachment.txt
1K   View   Download    
Temporary Error (500)   
We’re sorry, but your Gmail account is temporarily unavailable. We apologize for the inconvenience and suggest trying again in a few minutes.
If the issue persists, please visit the Gmail Help Center »
Try Again Sign Out
Show Detailed Technical Info
Numeric Code: 54

=====
Test 3: Attempts to send @include_file = 'c:\\temp\\attachment.zip' fail...

xp_startsmtp @return_code = 0
xp_sendmail @return_code = 104
Execution time: 2.487 seconds

Here is the attachment.txt file...

This is line 1 of 2 in attachment.txt.
This is line 2 of 2 in attachment.txt.

Here is the code used for Test 1, and modified as discussed above for Tests 2 and 3 (the smtp auth password value is not shown); this code DOES work when the attachment is omitted:

BBEGIN
DECLARE @return_code           INTEGER;
DECLARE @smtp_sender           LONG VARCHAR;
DECLARE @smtp_server           LONG VARCHAR; 
DECLARE @smtp_port             INTEGER; 
DECLARE @timeout               INTEGER;
DECLARE @smtp_sender_name      LONG VARCHAR;
DECLARE @smtp_auth_username    LONG VARCHAR; 
DECLARE @smtp_auth_password    LONG VARCHAR;
DECLARE @trusted_certificates  LONG VARCHAR;
DECLARE @recipient             LONG VARCHAR;
DECLARE @subject               LONG VARCHAR;
DECLARE @message               LONG VARCHAR;
DECLARE @include_file          LONG VARCHAR;

SET @smtp_sender          = 'Breck.Carter@gmail.com'; -- full email address for gmail
SET @smtp_server          = 'smtp.gmail.com';  -- smtp.gmail.com for gmail
SET @smtp_port            = 587;  -- 25 for standard SMTP, 465 or 587 for gmail
SET @timeout              = 10;   -- default is 60 seconds
SET @smtp_sender_name     = 'Foxhound';
SET @smtp_auth_username   = 'Breck.Carter@gmail.com'; -- full email address for gmail
SET @smtp_auth_password   = '...';
SET @trusted_certificates = 'c:\\temp\\equifax.cer';
SET @recipient            = 'bcarter@bcarter.com';
SET @subject              = STRING ( 'test subject at ', CURRENT TIMESTAMP );
SET @message              = STRING ( 'test message at ', CURRENT TIMESTAMP );
SET @include_file         = 'c:\\temp\\attachment.txt';

@return_code = CALL xp_startsmtp ( 
   smtp_sender          = @smtp_sender,  
   smtp_server          = @smtp_server,  
   smtp_port            = @smtp_port,  
   timeout              = @timeout,
   smtp_sender_name     = @smtp_sender_name,
   smtp_auth_username   = @smtp_auth_username, 
   smtp_auth_password   = @smtp_auth_password,
   trusted_certificates = @trusted_certificates );

MESSAGE STRING ( 'xp_startsmtp @return_code = ', @return_code ) TO CLIENT;

@return_code = CALL xp_sendmail ( 
   recipient     = @recipient,  
   subject       = @subject,  
   "message"     = @message,
   include_file  = @include_file );

MESSAGE STRING ( 'xp_sendmail @return_code = ', @return_code ) TO CLIENT;

CALL xp_stopsmtp(); -- do not bother to check return code

EXCEPTION WHEN OTHERS THEN
   CALL xp_stopsmtp();

END;