IMAP Base64 (RFC 3501)

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In this guide

This standards reference on Base64Encoding explains imap in plain language for developers and everyday users.

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IMAP mailbox names that contain non-ASCII characters use modified UTF-7 (RFC 3501). Inside those names, a Base64-like alphabet encodes Unicode with two important differences from RFC 4648:

Value Standard Base64 IMAP variant
62 + +
63 / ,
Padding = required none

The / character is replaced with , because / is the IMAP hierarchy separator. Padding is omitted so mailbox names stay compact.

Example

ASCII mailbox names need no encoding. A name with non-ASCII characters embeds &…- segments where … is IMAP Base64 of UTF-16BE bytes.

When developers need this

  • Debugging mailbox names returned by IMAP servers in Europe (umlauts, accents, Cyrillic).
  • Migrating mailboxes between providers.
  • Writing IMAP clients that round-trip international folder names.

Use the standard detector to recognise IMAP Base64, then normalize to standard Base64 or decode with the IMAP standard selected.

Ofte stilte spørsmål

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What is the fastest way to try imap?

Open the homepage Base64 converter or the related tools linked on this page and paste a sample.

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