Lost in all the technical jargon? Find definitions for common email and technical terms and learn more with our related resources.

PHP language

PHP language, initially called Personal Homepage but now a recursive acronym for PHP: Hypertext Preprocessor, is a scripting language embedded in HyperText Markup Language (HTML) for web pages. It’s used to develop web servers.

POP server

Post Office Protocol (POP) is a standard protocol, like Internet Message Access Protocol (IMAP), responsible for retrieving emails from an email server to deliver them to recipients’ inboxes. A POP server is a special type of email server responsible for syncing Gmail messages with compatible email clients, like Apple Mail, Microsoft Outlook, or Thunderbird. It allows recipients to use single sign-on for all email accounts, providing them access to all their email accounts from one email client.


Also known as an allowlist (formerly whitelist), passlists are lists of email addresses, IPs, and domains that are allowed to bypass certain security measures, such as spam filters.

Personal Folders File (. PST)

A Personal Folders File (. PST) is a Microsoft Outlook file that stores data from emails, calendar events, and other items from a Microsoft Exchange mailbox. Storing the contents of an Exchange mailbox creates free storage space for incoming emails. This allows recipients to search emails and gives them the flexibility to design their own . PST system as per their needs, allowing them to organize their space the way they prefer it like combining inboxes or splitting folders.

Personalized email

A personalized email is a message tailored to each individual user. Brands draw on customer data like their behavioral aspects, geographic location, or demographics to create personalized emails catering to customers’ needs. Customers are more likely to be interested in emails that speak to their requirements, boosting the brand’s user engagement metrics.


A postmaster is a mail server’s administrator and has the associated email address Mail servers route messages about errors in email sending or processing to this email address. Every domain that supports the Simple Mail Transfer Protocol (SMTP) for sending emails must have a postmaster address setup.

Public key cryptography

Public key cryptography, also known as public key encryption or asymmetric cryptography, is the process of using a pair of keys to encrypt data. While one key is a public key, the other is a private key that’s stored internally. These keys are used to authenticate a sender’s identity or encrypt data.


Python is a general-purpose scripting language that’s often used in web application development, desktop application, and data analysis. Developers also use Python to integrate with APIs from email service providers (ESPs). For instance, you can write a Python script to integrate Mailgun’s Email API with your web application. You can also script your email sends and take advantage of Mailgun’s powerful email deliverability features, email list management tools, and send-time optimization functionalities.