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I am completely new in AWS and I want to know about port 25 to send SMTP mail. My organisation is using one SMTP relay server which is having only one port 25, no any other port is available. I have an application (written in flask) which i will deploy on AWS and will use it to send SMTP mail using my organisation's server to outlook. Now, i want to know whether port 25 is blocked or not and can it be used in this scenario or not.

Thanks in advance.

Debartha Mitra
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    https://aws.amazon.com/premiumsupport/knowledge-center/ec2-port-25-throttle/ – Joachim Isaksson Jul 30 '20 at 10:35
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    Does this answer your question? [Why does Amazon EC2 limit port 25?](https://stackoverflow.com/questions/34694978/why-does-amazon-ec2-limit-port-25) – Adiii Jul 30 '20 at 10:53

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This is blocked on purpose by Amazon.

If the email provider supports another port you're advised to use this, however it seems for your use case you're limited.

In this case you will need to follow the instructions that are available on the How do I remove the restriction on port 25 from my EC2 instance? page. This will require you to fill in this form specifying your business case for why it needs to be unblocked.

Chris Williams
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  • thanks for replying back. So, in my scenario I will use my application deployed on AWS, to connect with organisation's SMTP relay server (which uses port 25 only) first and then send mail to organisation's outlook mail box. So, if i remove the restriction on port 25 , will this scenario work ? – Debartha Mitra Jul 30 '20 at 12:38
  • Yes this is correct, you will be able to use another port. 465 and 587 are commonly used :) – Chris Williams Jul 30 '20 at 12:43
  • I mean I need to use only port 25 as my email relay server only uses this. The scenario I told you just, there can I use deployed application to send request to my relay server after removal of restriction on 25 ? – Debartha Mitra Jul 30 '20 at 12:50
  • Oh right, yes once this is removed you can access outbound traffic using port 25 :) – Chris Williams Jul 30 '20 at 13:08
  • No problem , hope it all goes well :) – Chris Williams Jul 30 '20 at 13:17