Gmail SMTP is not working in ec2 instance
MAIL not accepted from server
Because of the spam abuse that has historically been sent from people using EC2 instances, virtually ALL popular mail providers block the receipt of email from EC2 instances. The world of email and anti-spam measures is part-technical, part-political. For this reason, AWS offers Amazon Simple Email Service.
AWS works with mail providers to ensure that the nodes used by SES have been whitelisted because we do proper authorization/verification up-front.
In this case, the ability to send email from one server but not AWS is, in all likelihood, due to EC2's IP range being blacklisted by Google.
Authentication Required
If the same user/pass works elsewhere without changes, I'm not sure what to say. I know that lots and lots of mail traffic no longer uses port 25, opting instead for 587 for non-SSL and 465 for SSL. That's the first place I'd start poking to find a solution.
This has nothing to do with your ec2 instance (unless the relevant outbound ports are closed) but with the fact that Gmail really doesn't like a connection it can't identify. As stated in the thread, make sure you go to https://www.google.com/settings/security/lesssecureapps.
Then, once your instance tries to connect to the SMTP server (by sending an email in your web app I suppose), connect to your mail client with the gmail account credentials used for the SMTP connection (Gmail, thunderbird, whatever you normally use). You will have then received an email from google stating that there was some suspicious activity and that they blocked the connection, just tell them that the ec2 instance IP was indeed you and you will be all set.
Using a TLS connection (port number: 587) on AWS Lambda.
How I solved the problem:
- In your GMAIL account, turn on 2-factor authentication. This can be found under security settings when you go to general settings for your account.
- Create a new App Password. (The field is right below the 2-factor). You can call it whatever you want. Just make sure to copy it.
- Use that for your previous password.
I did that and I can send emails from AWS Lambda with no problem.
Note: You can't have "Less Secure Apps" turned on for this option. This will require you to use the App password for every application you use this email for. I had to make a few different passwords for the different apps that I use a random Gmail account for.
I got the idea from SMTP Authentication Error 534.