Postfix giving me "SMTP server error: 5.5.0 Sender already specified"
 

Hi,

I'm using postfix to send some mail from my cloud server via a web page on my website that uses PHPmailer to do SMTP authentication. My cloud server has a dedicated IP for all inbound and outbound data. The problem I am having is that it sends roughly 75 - 100 messages successfully before it returns the following error for the remaining few hundred recipients in my list:

SMTP Error: The following recipients failed: example@example.com Mailer Error (example@example.com) SMTP Error: The following recipients failed: example@example.com SMTP server error: 5.5.0 Sender already specified

Anybody ever come across this before? What on earth is happening here?

Thanks,
Josh

Welcome to LinuxQuestions! You defiantly have a tough one here.

I am assuming your trying to relay mail from one server to another. Make sure you have the mail server setup to allow relay on your internal network. If it is not internal and you don't control the server you will probably not be able to do this since most online mail servers have admins that refuse to allow relay due to spammers.