The route of an email does not follow a straight line: it usually does not go directly from the sender to the recipient, but rather completes several intermediate steps in a clearly regulated process. The main actors are the SMTP servers service involved, which strictly follow the necessary protocol to ensure that the email reaches the recipient . On the Internet there is an entire network of these distribution stations or relays (relays), which make possible the traffic of emails.
What is an SMTP server and what is it used for?
An SMTP server is a mail server that transports email from a sender to one or more recipients on the Internet and forwards them according to the regulations of the SMTP network protocol . An important function of the SMTP server is to prevent spam, by employing authentication mechanisms , through which only authorized users can send emails. To do this, most modern mail servers support the ESMTP protocol extension with SMTP authentication .
SMTP servers are the essential link for successful email transmission , involving multiple servers: the sender’s outgoing mail server, one or more external forwarding servers, and the recipient’s incoming mail server.
Sender’s outgoing mail server
After the sender has sent their email, the provider’s webmail application or mail program (the SMTP client, also called “ Mail User Agent “, or MUA for short) converts it into a header and body and uploads to the outgoing mail server, an SMTP server (or SMTP server). This server has a so-called “ Mail Transfer Agent ” (MTA), which is the software base for sending and receiving emails. The MTA checks the size and spam of the mail and then saves it. To ease the burden on the MTA, a “ Mail Submission Agent ” (MSA) is occasionally installed, which checks the validity of the mail beforehand. The MTA then searches the “Domain Name System” (DNS)the IP address of the recipient’s mail server.
External forwarding server
If the recipient’s domain is connected to the same mail server as the sender, the email is delivered directly. If this is not the case, the MTA breaks it into small data packets, which are forwarded to the destination SMTP server via the shortest path with the least traffic. Packets sometimes pass through multiple MTAs on external SMTP servers (called “relays” in technical jargon), which handle continuous forwarding.
Recipient’s incoming mail server
Upon reaching the destination SMTP server , the data packets are reassembled to form a complete email. The MSA and/or MTA check for spam one more time and then transfer it to the Inbox server’s message store. From there, the so-called “ Mail Delivery Agent ” (MDA) transfers it to the recipient’s email inbox. Other network protocols, such as IMAP or POP3 , then download the email to the recipient’s SMTP client.
Technically, it would also be possible to send an email directly from the sender’s SMTP client to the recipient’s client. However, using an SMTP server offers a distinct advantage: If the recipient’s incoming mail server is busy or temporarily down and the email cannot be delivered, the responsible SMTP server automatically tries to deliver the email at regular intervals . regular. This happens until the delivery is successful or until the mail is returned to the sender as undeliverable.
What SMTP mail servers can I use?
As a sender, you basically have the option to choose between SMTP servers from different providers to transport your emails to the network and forward them. Another interesting alternative for many is to set up your own server.
Provider SMTP server
dedicated smtp server for bulk mailing from established providers are also recognized as trustworthy by other providers. Furthermore, its anti-spam filters are considered particularly strong due to the large amount of data processed. However, for free offers, you usually have to set strict limitations on the number of emails per day, size of attachments, and mailbox storage space.
The offers are presented from different points of view:
- Internet Service Providers — Internet Service Providers (ISPs) such as IONOS often offer an email address in addition to an Internet connection, with which the company’s own SMTP client servers can be accessed.
- Email Providers — The most typical way for individuals to email friends and family is to use a free email provider’s email application such as Gmail or Yahoo. The only requirement is an email address that matches the domain, with which the provider’s SMTP server can be used for personal correspondence. All you have to do is configure the mailbox to have the correct SMTP server address. Later in this article you will find an overview of the most popular providers and their addresses.
- Hosting service providers — Many hosting packages, such as those from IONOS, contain a standard SMTP server, which can be used to handle internal and external mail traffic.
- Specialized Providers — Some companies have specialized in renting SMTP servers. These include Amazon SES and SparkPost, for example, where hardware can be rented on demand.
Own SMTP server
With some basic technical knowledge, you can also set up your own SMTP server . For example, you can set one up with a Raspberry Pi with the appropriate software.
The advantages are obvious: you will not have restrictions on use by a single provider, you will enjoy full control over all settings and maximum data sovereignty . Also, a self-built server is perfectly adequate for getting to grips with the background of email traffic. However, there are also disadvantages: Due to the dynamic IP address of private Internet access, private SMTP servers are often classified as spam distributors by large mail providers. This problem can be solved with some restructuring measures and/or additional costs, so if you just want to send emails to another private client, your own SMTP server is a good alternative.
Advantages and disadvantages of SMTP servers at a glance
The following chart is a summary of the advantages and disadvantages of providers’ servers, compared to self-configured servers:
What is my SMTP server and how to find it?
If an error occurs in the transmission of an email, it is often easier to solve the problem if you know the address of the SMTP server used. Since most addresses are structured in the form “smtp.domain.es” or “mail.domain.es”, they are relatively easy to remember.
You can find out which is the correct address for your email account in your mail client settings :
- In Outlook, click “ Account Settings ” on the File menu, select your account, and click “ Change ”. An overview of the user, server and credentials will open.
- In Mozilla Thunderbird , right-click your account to open the menu and click “ Settings ”. In the menu option “ Outgoing mail server (SMTP) ” select your mail server and click on “ Edit ”.
If you need your SMTP server address for the first time, for example when manually configuring your mail program , you’ll find it in the help section of your provider’s home page . The following is an updated list (January 2019) of the main email providers and addresses of their publicly accessible best smtp service provider:
How can I test an SMTP server?
Having the correct SMTP server address is also necessary if email transmission is not working properly and measures such as checking the connection mode of the mail client or emptying the inbox have not brought about any improvement. The Telnet tool , which is available on all common operating systems, can provide you with the information you need.
