IMAP Concepts

IMAP is a surprisingly simple protocol to implement, particularly in an environment like the Developing in the Translator. Here are some basic concepts:

It’s a protocol intended to let a email program communicate and get email from a email server.

A TCP/IP stream gives guaranteed delivery of the order of data.

Guaranteed means the TCP/IP protocol is designed to try and help the data reach the other side back and forth in a way that the data and order of the data is preserved.

IMAP is a conversation between the client and the server. The client and server talk to each other using the language of IMAP.

This is a common pattern with many TCP/IP protocols - it’s a way for the server to say - Hi - I speak your language and let’s begin a conversation.

It’s like going up to someone and saying Hola! It signals you are ready for a conversation and that you speak Spanish.

This is what we’d see say with a Gmail IMAP server:

* OK Gimap ready for requests from 69.196.142.158 ql9mb2511069qvb

This is IMAP for Hello!

We need to authenticate - usually with a user name and password. We send a LOGIN command which looks like this:

a01 LOGIN aryn.wiebe@interfaceware.com lkjllkjddkdjsfdhgh\r\n

So IMAP messages start with a unique code for each message we send to the server. In this case a01 - this unique ID that we use to track the command we have sent so when we get a reply from the server then we know what the topic was.

Notice the \r\n newline sequence? There is an interesting story behind that.

Remember that question I asked you?

* CAPABILITY IMAP4rev1 UNSELECT IDLE NAMESPACE QUOTA ID XLIST CHILDREN X-GM-EXT-1 UIDPLUS COMPRESS=DEFLATE ENABLE MOVE CONDSTORE ESEARCH UTF8=ACCEPT LIST-EXTENDED LIST-STATUS LITERAL- SPECIAL-USE APPENDLIMIT=35651584
a01 OK aryn.wiebe@interfaceware.com authenticated (Success)

Take special note of the a01 OK.

The ID matches up with the ID we sent before as the client - so this is part of the conversation of telling the client whether the last command it sent was OK or refused NO, or was formatted incorrectly - i.e. BAD an error.

So IMAP clients typically need a method of generating these IDs either randomly or in sequence.

An IMAP client also needs a routine to read the data back from the client to get the data.

It’s a conversation after all - no two conversations are alike.

Line 8 tells us we have successfully selected the INBOX.

Line 4 also tells us the highest ID mail which exists is 82838.

* FLAGS (\Answered \Flagged \Draft \Deleted \Seen $NotPhishing $Phishing)
* OK [PERMANENTFLAGS (\Answered \Flagged \Draft \Deleted \Seen $NotPhishing $Phishing \*)] Flags permitted.
* OK [UIDVALIDITY 1] UIDs valid.
* 82838 EXISTS
* 0 RECENT
* OK [UIDNEXT 84128] Predicted next UID.
* OK [HIGHESTMODSEQ 8669111]
a02 OK [READ-WRITE] INBOX selected. (Success)

Here is a sample of an IMAP Fetch response:

Note we can clearly see the header, body, and success response all separated by a boundry (001a113da73205a6ea056272f2ab). We can use this boundary to help parse the email and isolate its parts.

* 1 FETCH (BODY[] {4835}
MIME-Version: 1.0
x-no-auto-attachment: 1
Received: by 10.25.43.137; Wed, 10 Jan 2018 13:45:09 -0800 (PST)
Date: Wed, 10 Jan 2018 13:45:09 -0800
Message-ID: &lt;CAP14fq11RQ3+xEZk7uSmWb4rv1oEDdX66fuq7wJJbkxFv+u1fA@mail.gmail.com&gt;
Subject: Hey!
From: real.person@gmail.com;
To: Aryn Wiebe &lt;aryn.wiebe@interfaceware.com&gt;
Content-Type: multipart/alternative; boundary="001a113da73205a6ea056272f2ab"

--001a113da73205a6ea056272f2ab
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

Hi Aryn

This is a sample email! 

Thanks, 

--001a113da73205a6ea056272f2ab
Content-Type: text/html; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

<!DOCTYPE html>
...

--001a113da73205a6ea056272f2ab--)
a03 OK Success

Lot’s of commands are possible like getting a summary of an email (can be helpful to avoid loading a very big email).

You can delete emails.

You can probably filter on them. Ask Chat GPT - it knows a lot about IMAP

You’ll never get a better way to see how IMAP really works.

Load the IMAP Email Feed and use The string viewing window and Annotation Windows you really get to see how it works.

That’s important since it’s also how you can diagnose problems.

I don’t know about you but I get very frustrated with the spinning disc I often get on my Apple Email client on my phone with no visibility as to what is going wrong.