Notes

NitroMail.io
When a user within an organization sends an email, a lot happens behind the scenes. When NitroMail.io send, the message is handed off to a service running the simple mail transport protocol (SMTP). It is the job of the SMTP service to get hold of the recipient mail server and transfer the message to the mail server. If the SMTP service stops responding, mail cannot be sent.

There are many reasons a mail server could lose its ability to send mail. Listed below are just a couple:

1. The mail server could lose its link with the Internet.

2. The mail server could go out of resources (like disk space) which can cause the operating-system to crash or hang.

3. A mail administrator will make a configuration error that may cause the service to become confused about how exactly to send mail.

4. A mail server could possibly be added to a blacklist preventing it from sending mail to any recipient server using that blacklist as resource to remove spam.

Since outgoing mail is a function that is crucial for almost every organization, it is very import to have in place some method to monitor the service. Some website monitoring services provide support for monitoring SMTP. Here's how it works:

First, the web site monitoring service will attempt to establish a socket connection with the SMTP server utilizing the transmission control protocol (TCP). This involves sending a SYN packet to the SMTP server and looking forward to an ACK packet in response. If no ACK is received, the monitoring service knows that the SMTP service is not responding to requests.

Next, assuming the ACK was received and a socket connection has been successfully create, the monitoring service will attempt to communicate using protocol commands. Here's one way which could work (you can attempt this out on your own using the well-known terminal program Telnet):

1. If the bond was established, the mail server will respond using its banner, usually something similar to "Linked to mail.somedomain.net." If no banner is received, something is probably wrong.

2. Next, the monitoring service will introduce itself in the same way if it were a mail user by sending the "HELO" command accompanied by an origin domain for the e-mail. So the complete command might look like "HELO my.domain.net."

3. If all is going well, the SMTP server will respond with something similar to "250 Hello my.domain.net, very happy to meet you."

At that point it really is established that the SMTP server is giving an answer to connection requests and is ready to receive more commands. If the monitoring service notices a failure at any of these points it could log the failure, the time, and any content that has been received which may help diagnose the problem. The service will then distribute alerts by email, SMS text as well as using a real telephone call.
My Website: https://www.reviewsis.com/email-advertising-telltale-indicators-that-your-smtp-server-is-overloaded/