Email goes in spam when I send it via others SMTP server

Question

I\'m using PHP Swift_mailer library to send emails to my customers\' clients from behalf of customers. I use their SMTP server, port, login, pass:

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Answer 1

If you've not done so already, you might want to setup an SPF record for the domain that you are sending from, to indicate that the sending mail server's IP is authorized to send mail for your domain. If you don't already have an SPF record setup, this might solve the problem.

Also - To see if the outgoing SMTP server that you are using has a glaring problem that would cause receiving mail servers to think it's a spammer, try sending a message from your application through your outgoing SMTP server to check-auth@verifier.port25.com. This service will do a bunch of checks, and you'll get a report back with ton of information, such whether or not your mail server's DNS is setup correctly, whether your mail server's IP is on any black lists, if you have a problem with your SPF records, etc.