IMAP lets apps read and organize mail on the server, while SMTP sends it.
Key points
- IMAP4rev2 is specified in RFC 9051 (2021), which updates the long-standing IMAP4rev1 in RFC 3501 [1][2].
- Messages stay on the server, and clients sync folders and flags such as Seen, Answered and Flagged, unlike older download-and-delete POP3 setups [1][4].
- RFC 8314 recommends implicit TLS on port 993 for IMAP access [3].
- IMAP handles reading and organizing mail only; outgoing mail uses SMTP [1].
- Tools that offer Email Sync or Reply Detection often read a mailbox over IMAP or a provider API such as the Gmail API or Microsoft Graph.
What IMAP does
IMAP treats the server as the source of truth. A client logs in, selects a mailbox such as INBOX, and fetches message headers, bodies or parts on demand [1]. Changes made on one device, such as marking a message read, moving it to a folder or deleting it, are stored on the server and seen by every other client. RFC 9051 defines commands including SELECT, FETCH, SEARCH, STORE and MOVE, and the IDLE extension lets a client be told about new mail without polling [1]. The previous version, RFC 3501, remains widely deployed, and servers commonly support both [2]. This design is what makes it practical to use one mailbox from a phone, a laptop and a connected application at the same time.
Security and authentication
Because IMAP carries full message contents and credentials, it should always run over TLS. RFC 8314 declares cleartext access obsolete and recommends implicit TLS on port 993 [3]. Large providers increasingly require OAuth-based sign-in rather than a plain password, so an application asks the user to grant access through the provider's consent screen and receives a token instead of storing a password; see OAuth. Access can usually be revoked from the account's security settings at any time. When evaluating any tool that connects to a mailbox, check which permissions it requests and whether it needs read access, send access or both, since those scopes decide what it can do with your Email Thread history.
IMAP in outbound workflows
For Cold Email and sales tools, the receiving side matters as much as sending. Reading the inbox lets software detect replies, spot bounce messages, stop an Email Sequence when someone answers and keep conversations threaded using the Message-ID and References headers. The Wikipedia overview describes how IMAP clients track message state with unique identifiers, which is what lets a tool resume where it left off [4]. PineLead sends from your own connected mailbox and replies land back in the same thread, so conversations stay in your normal inbox rather than in a separate system, and you can answer them there or pass them to your CRM (Customer Relationship Management).
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