Get Bounce with Error 550 Action Not Taken

just installed updated MailWizz(1.8.3) application in my NameCheap VPS server with PowerMTA , SendGrid SMTP, MailGun SMTP and configure everything but when i blast email Campaign then after few send i start getting error and all emails getting start bouncing, the Bounce error Code is :

"failed,5.0.0 (undefined status),smtp;550 Action not taken"

this error for every ISP's like yahoo, gmail, hotmail or any other ISP, i getting this issue only with only Maiwizz however i use other email application (Like Interspire or Mumara) working perfectly with out any trouble and issue.

i had try it with PostFix, EXIM, SendMail, Qmail and Other Existing SMTP Provide like SendGrid, Mailgun, AWS-SES and SparkPost too but every time i getting same Error (i getting error only when i schedule a Campaign).

I know this issue. I agree with Postfix Exim or PMTA . but i never think you got same error with ESP such as Sendgrid because of there isn't way to get that.

Also Its not problem with Mailwizz. Even you use Interspire / Mumara or any other mailer you will get this problem. So i never agree with you.

What is your Host Provider ?
There are two Reasons for this.
1.Your host provider ( server provider ) blocked your message. So it's bouncing with "smtp;550 Action not taken"
Specially when you use Host provider such as Name Cheap you will face this issue. As i know they use Spam Expert to filter.
You can create ticket on Name Cheap and get fix it. But make sure you have Configured Your SMTP as well as.

Because Gmail Does not bounce / reject email with that dsn code.

Best thing is that you can try another host provider and check issue.
But let see here
"failed,5.0.0 (undefined status),smtp;550 Action not taken"

This is from your first comment, and this is default pmta log file data format.
So i never think you got same error with each ESP.

Namecheap use your ips for their mailing. So their IPs have good reputation.
They want to make sure that you will not send spams or due to complains ip reputation get reduce. That's why you need to contact them. then they ask some questions.

Then they will check your mail headers and they will whitelist your sending domain or sending email.

Also you will possible to face similar issue on another host provider who use Spam Expert as their Spam filter.