Often, administrators managing their on-premise email server wonder if they need a valid SSL certificate for their server to communicate with the outside world. In this article, we not only discuss the importance of an SSL certificate but also explore when a self-signed certificate can be used as an alternative.
Before diving into the subject, let's briefly discuss how SMTP works. Emails go through multiple SMTP servers before reaching their final destination. The sending server acts as an SMTP client, and the receiving end acts as an SMTP server. Your SSL certificate only comes into play when your server is acting as the SMTP server. Refer to the image below.
In the above image, every server (colored in blue) has two ends: sending and receiving, colored in yellow and green, respectively. The receiving ends for every server are labeled R1, R2, and R3. The sending ends are labeled as S1, S2, and S3. When an SMTP client connects to an SMTP server, the SSL certificate used on the server becomes relevant. A certificate is not needed on the SMTP client. This is similar to HTTP, where a web server requires an SSL certificate, but a browser (acting as a client) does not.
Here is the flow of events:
As a rule of thumb, keep the following rules in mind:
When using Xeams, you have several options regarding an SSL certificate.
Please refer to this page for details.
Although SSL certificates are required for any email server, there are instances when you can get away with a self-signed certificate or no certificate at all. A certificate provides two benefits: it encrypts the data during transfer and ensures the sender that the receiving end is authentic. These benefits diminish to a certain extent when the communicating parties are inside a trusted network.