Productivity
Most e-mail services allow you to use the "+" notation to create sub-addresses that are automatically forwarded to your main e-mail account.
In 1969, the RFC (Request for Comments), a series of reviews/reports on network technologies, was published for the first time. These publications serve to describe the technical characteristics of network technologies, such as ARPANET and then the Internet, and sometimes become standards. In 1982, the group, among other things, looked into email addresses, which would allow for easy contact with an individual from one part of the network to another. In their initial specification, they allowed for example the use of printable characters: !#$%&'*+-/=?^_`|~}{. However, it is unlikely that you have seen many addresses with these characters. This is explained in part by the fact that these RFCs, even though they are authoritative in the field, are not necessarily adopted as standards. As a result, most email services will forbid you from creating an address with these special characters. However, it is not impossible in theory. Most often, the sites where you register your address will check its validity, and the problem lies with them, as the sites do not comply with the RFC. New RFCs have updated the specifications, but it remains that these characters could theoretically be used.
As you may have noticed, the "+" character was considered acceptable in an email address in 1982. Moreover, as indicated, the final decision on the processing of emails and their validity actually rests with the address provider. Thus, from 1998, perhaps earlier, some individuals begin to use the notation with a plus, as email servers like QMail treat these addresses in a special way. The software receives an email, then analyzes the address to determine where to send it. Emails are broken down into two main parts: the local part, which comes before the at sign, and the domain, which comes after. Some email servers also begin to separate what comes before the plus sign from what comes after. What comes before represents the real local name, while what comes after the plus becomes a sort of label or sub-address. In other words, if I send an email to [email protected] and another to [email protected], John Doe will receive two emails in his inbox, because the second address is redirected directly to the first. However, even though the addresses eventually end up in the same inbox, the address listed as recipient remains the one that was used. It is then possible to see that the email was sent to [email protected] and not by the default address. This also means that it is possible in your email service to establish filters that automatically classify your emails into folders based on the recipient to whom the email was sent.
This notation can be used in most services, such as Gmail, Apple's iCloud, Outlook.com, ProtonMail, etc. One of the most frequent uses, and old if we rely on an email from 1998 and a blog post from 2002, is to use the notation to sign up for websites. Anders Jacobsen describes how he signs up for different services with addresses in the following format: [email protected]. In this perspective, John Doe signing up for Twitter today would do so with the address [email protected]. The reason he uses this strategy is that it allows him to quickly identify the sources of spam. If he starts receiving dubious messages at this address, he will know that his address may have been used in spam chains. He will then only have to block emails sent to this address and will know where the disclosure of his email address came from. The other use is simply to automatically classify his emails. For example, you could create a folder in your email service, then redirect all emails from a sub-address into this folder. One can then imagine a plethora of possible uses. Examples:
In this last example, I have no difficulty imagining a professor creating a folder bearing the acronym of his course, then asking students to send him an email at [email protected] for their questions or submissions. In short, your simple email address actually contains an infinite number of sub-addresses to simplify your life and the management of your communications.
Note: If you plan to change your email provider, check that it accepts this notation; otherwise, all your sub-addresses will not be transferred to you.