It is important to note that MTA-s do not have to communicate with each other over TLS/SSL. MTA uses SMTP and deals with receiving messages and relaying messages. When STARTTLS is not available and the mail client is not forced to use a secure mail exchange protocol then the email is exchanged in plaintext, i.e., in an unencrypted form.Ī message transfer agent (MTA) is used to relay emails from one mail server to another. However, STARTTLS is mostly supported by the major email providers and many servers still do not provide this option. Some SMTP servers support STARTTLS which enables to automatically switch from an unencrypted connection to an encrypted connection over SSL / TLS. In addition, as the content of the mail is not end-to-end encrypted, the mail servers are able to read the contents of the emails. It might be possible to encrypt the links between the mail clients and mail servers but while the mail is routed through the Internet it might pass servers that do not support encryption. However, these protocols are still alive and it is difficult to modify them or to replace them with more secure protocols.īy default email is not encrypted, some links between the mail servers might be encrypted but this does not mean that the content of the email can not be intercepted, read and modified. These protocols were designed to get the job done in an environment where security was not so relevant. The protocols that are used to exchange emails are not designed to take security and privacy seriously.
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However, if a mail server does not support STARTTLS, then the user will have to configure the email client software to use a port that provides an encrypted connection. Most well known email providers have enabled support for STARTTLS. STARTTLS adds SSL / TLS by default if the corresponding mail server supports this. There is a feature that enables encryption even for the plain SMTP, IMAP, POP3 and this feature is called STARTTLS. Most email servers support the secure versions of these protocols but the user may have to configure the email client software to use the correct port. It is obvious that the extra S in the abbreviations stands for secure and it just means that the protocol is used inside of a SSL / TLS session. Secure POP3 is called POP3S and it uses port 995. Secure IMAP is called IMAPS and it uses port 993.
Secure SMTP is called SMTPS and it uses port 465. Special ports are reserved for these protocols to transmit data over SSL / TLS. Actually, all of these protocols support the transmission of data over SSL / TLS but this is an optional feature. One might wonder if SMTP, IMAP and POP3 always encrypt the email traffic in order to protect confidential information from leaking. However, POP3 is an older protocol that first fetches the mail and then deletes it from the server which means that by default mail can be downloaded to a single device. Therefore, with IMAP it is possible to view emails in both the smartphone and in a laptop without the emails being deleted from the server. IMAP protocol is commonly used nowadays as it provides support for multiple simultaneous clients. In order to receive emails client software uses either IMAP or POP3. However, email client software is commonly configured to use SMTP only for sending emails. Simple Mail Transfer Protocol (SMTP) is used to transmit emails both between the user and email server and between the mail servers. Secure email exchange How email exchange works
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