SMTP Emails go into SPAM on Outlook

The first and most obvious reason for your emails ending up in spam is because your recipients put them there. Even if your content is strong and the recipient expressly gave you permission to contact them, they may still decide to mark your email as spam as a way to clean up a cluttered inbox

SMTP Emails go into SPAM on Outlook

The first and most obvious reason for your emails ending up in spam is because your recipients put them there. Even if your content is strong and the recipient expressly gave you permission to contact them, they may still decide to mark your email as spam as a way to clean up a cluttered inbox

You cannot simply use random mail addresses and hope it works. Spam countermeasures may check whether or not the sending server is actually allowed to send mails from that address. Google "Domain Keys" or "SPF" to see two existing methods to authenticate the sending of emails. I assume that your server is not allowed to send mails from the "@gmail.com" domain, so anyone is doing the right thing flagging these as spam.

Additionally, spam detection is analyzing the mail contents. And this might also be individually configured because everyone's spam is different. You stating that "outlook.com" recognized your mail as spam might be because you flagged emails as spam earlier that looked just like the one you are sending now. A different account might see this mail as valid.

If the receiving mail service does not inform the recipient about why this mail was flagged as spam, there simply is not very much you can do. But it's not SwiftMailers fault or related to your setup.