SMTP

openssl s_client -connect smtp.example.com:465

openssl s_client -starttls smtp -connect smtp.example.com:587

https://mailtrap.io/blog/2016-07-26-how-to-test-smtp-server

telnet mail.example.com 25
EHLO server.example.com
MAIL FROM: <test@example.com>
RCPT TO: <test@example.com>
DATA

MX Toolbox

MX Toolbox is a free service that will perform simple tests of:

• SMTP Reverse DNS Mismatch
• SMTP Valid Hostname
• SMTP Banner Check
• SMTP TLS
• SMTP Connection Time
• SMTP Open Relay
• SMTP Transaction Time

However, you are not allowed to define the port, enter password etc. The number of tests is also limited.

Wormly

Wormly gives you a free trial to check your SMTP servers, but does not allow defining the port or password, a secure connection is also not available.

SMTPer

SMTPer is indeed the most convenient solution that allows defining the port, provides users with a secure connection and authorization. You also can fill out both sender and recipient forms.

test-smtp.com

Test SMTP simply sends requests to SMTP servers to perform Relaying tests. This service does not have a sufficient toolkit for a proper SMTP examination.

testsmtp.tcsoftware.net

Check SMTP works for certain parts of a process but isn’t enough for a proper examination. Does not provide a secure connection.

Check SMTP will run the following tests:

• Check your server DNS Black List status
• Verify MX Records
• Relay Configuration
• PTR Record (Reverse Lookup)
• Verify Email Address