====== SMTP ======

==== Ports ====

^ 25 | SMTP |
^ 587 | SMTPS |
^ 2525 | non-standard port sometimes mirroring 25/587 |

===== testing =====

==== SMTPS (SMTP over TLS/SSL) ====
<code bash>
openssl s_client -connect smtp.example.com:465
</code>

==== SMTP over STARTTLS ====
<code bash>
openssl s_client -starttls smtp -connect smtp.example.com:587
</code>

==== SMTP without TLS ====

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

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

==== online tools ====

[[https://mxtoolbox.com/diagnostic.aspx|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.

[[https://www.wormly.com/test_smtp_server|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.

[[http://smtper.nanogenesis.fr/|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.

[[http://www.test-smtp.com/|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.

[[http://testsmtp.tcsoftware.net/|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