I have an application hosted in an Amazon EC2 Server that uses e-mail service from a shared web host. I did this to utilize the shared hosting e-mail server and the available e-mail administration tool and webmail interface.
My application uses amazon SES to send e-mail. I just authorized SES to send mails with my domain name (by adding some entries to my dns records and confirming I'm the domain owner), and this is working ok. When I need to send a mail, I connect to SES SMTP server and send it using PHPMailer.
Everything is working ok, except my mails are getting the DOS_OUTLOOK_TO_MX flag in SpamAsssasin's, making it sometimes be classified as spam.
What this flag means? Is there some way to avoid it?
Spamassassin DOS_OUTLOOK_TO_MX rule is fired when two internal flags are set by processed message: __DOS_DIRECT_TO_MX and __ANY_OUTLOOK_MUA.
__DOS_DIRECT_TO_MX flag means that the message was sent directly from sender email client to recipient MTA server. This is usually true for internal mail but can occur in your case when a recipient also uses Amazon SES for mail processing.
__ANY_OUTLOOK_MUA flag means that the message has X-Mailer =~ /^Microsoft (?:Office )?Outlook\b/ header.
Both internal flags are harmless by themselves but their combination leads to DOS_OUTLOOK_TO_MX with high spam score. You need to check X-Mailer header of messages sent with PHPMailer. This header should be set to PHPMailer, not to Microsoft Outlook or something similar.