FAQ (Frequently Asked Questions)
Frequently asked questions about Email Server
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Frequently asked questions about Email Server
An SMTP server is a computer or an app that is responsible for sending emails. It functions following the Simple Mail Transfer Protocol (SMTP). An SMTP server receives emails from the email client. Then it passes them on to another SMTP email server and relays them to the incoming mail server.
Take a look at the basic steps of the email sending route and what role the SMTP server plays. A mail user agent (MUA), which can be your email client or an app, connects to the SMTP server of your domain (for example, smtp.mailtrap.io) to start the SMTP connection. This is called an SMTP handshake. The connection is carried out via an SMTP port, which is normally 25. However, other ports, such as 465, 587, 2525 could also be used in different cases. You can learn more about them in our blog post about SMTP ports. Once connected, the SMTP session begins. The client submits the sender’s and recipient’s email addresses, as well as the email body and attachments, to the server. The SMTP server, or more precisely the mail transfer agent (MTA), checks whether the domain name of the recipient and the sender is the same. If it is, the email goes directly to the recipient’s POP3 or IMAP server. If the domains are different, the SMTP server has to communicate with the Domain Name Server (DNS). The DNS provides the recipient’s IP address. The sender’s SMTP server connects to the recipient’s SMTP server and relays the email. If the recipient’s server is not available (down or busy), the email will be put into an SMTP queue. This is a buffer where the emails are stored before they hit the endpoint. For more on this, read our blog post about email queuing. Alternatively, the email can be dropped to a backup server. The recipient’s SMTP server verifies the incoming email. If the domain and user name have been recognized, the server forwards the email to the receiving servers, POP3 or IMAP server.
Surprisingly enough, the SMTP server isn’t inherently secure. It doesn’t have any encryption or security mechanisms built into it. This makes it vulnerable to spoofing, spamming, or data leakage. To avoid all those unfortunate events, email providers have added security layers to the infrastructure. The first mechanism they incorporated was the Secure Sockets Layer (SSL) but it had significant security flaws. As a result, Internet Engineering Task Force (IETF) deprecated its final version, SSL 3.0 in 2015 by enforcing RFC 7568. 4 years after SSL’s creation, another security standard, Transport Security Layer (TLS) was introduced to the public. Initially, it wasn’t perfect either, yet it was improved throughout the years. As of 2022, the TLS 1.3 version is considered to be the safest protocol for email encryption. All of that is great, but at what point of the SMTP connection does TLS enter the game? By default, most email clients initiate a TLS connection during the handshake. They do so by using the SMTP command STARTTLS, which switches to an encrypted connection. To learn more, check out our blog post about SMTP security.
SMTP authentication or SMTP AUTH is the mechanism used to secure the outgoing email server. It’s the service provided by the Extended Simple Mail Transfer Protocol (ESMTP) which adds new functionalities to the SMTP protocol, including authentication. SMTP AUTH ‘‘demands’ that the sender is authorized to use the server to send emails. It makes it harder to impersonate real users, protecting them from spoofers and spammers. SMTP AUTH leverages the SASL mechanism for authentication, which specifies the level of security and login methods. Mechanisms such as PLAIN, LOGIN, and CRAM-MD5 are commonly used in that process. To dive deeper into SMTP authentication, check out our dedicated guide.
Your own SMTP server Setting up your own SMTP server might be an option if you want to send bulk emails. It imposes no limit on how many emails you send per hour/day and ensures control of all your outgoing mail. However, this comes with a drawback as the bounce rate can increase by 20-30%, which is a major consideration for the deliverability of transactional or email marketing campaigns. If you want to know all the ins and outs of setting up your own SMTP server, read this blog post.
In our guide about the best free SMTP servers, we introduced a list of cloud-based 3-rd party email APIs that most startups and projects opt for. These are SMTP relay services that include Gmail, Amazon SES, Elastic Email, Mailtrap, and others. The main benefit of using SMTP service providers instead of the local SMTP is that you don’t have to build and maintain the whole email infrastructure on your own. This means that you save your resources. However, it’s important to pick out a reliable email provider such as Mailtrap Email API. It’s an end-to-end solution that can safely deliver email messages to the recipients’ inboxes. It includes a bunch of useful features, such as actionable analytics, color-coded email categories, single-screen stats, webhooks, and dashboards. These can be used to track and control the deliverability of all your outbound emails.
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