You can use the Telnet program to enter the same commands an email client would issue to an Internet Message Access Protocol (IMAP) server, which can be helpful in troubleshooting problems related to connectivity to an IMAP server.
A telnet program is often available by default with
Linux and
OS X/macOS systems.
On an OS X/macOS system, you can run the program from a
Terminal
window; the program is found in the Applications folder. On a
Microsoft Windows system, you can use the free
PuTTY program or you can
install a Telnet client
from Microsoft Windows. With a telnet client that is uses a
command-line
interface (CLI), you can issue the command telnet server
imap where server is the
fully
qualified domain name (FQDN) of the IMAP server or the
IP address of the server.
Or you can use the
well-known port for the IMAP protocol, which is
TCP
port 143, i.e., telnet server 143.
When you connect to the server, you should see an "OK" reply; enter
the command A login username password
where username is the account name for the relevant account and
password is the account's password. That will verify you can log
into the account. You can then enter B select INBOX which
should return information about the inbox for the account followed by another
"OK" response. You can issue the command C logout to logoff the
IMAP server. You should see another "OK" response and be returned to the
shell prompt. E.g.:
$ telnet 127.0.0.1 imap Trying 127.0.0.1... Connected to 127.0.0.1. Escape character is '^]'. * OK [CAPABILITY IMAP4rev1 LITERAL+ SASL-IR LOGIN-REFERRALS ID ENABLE IDLE START TLS AUTH=PLAIN] Dovecot ready. A login nell ASecretPassword A OK [CAPABILITY IMAP4rev1 LITERAL+ SASL-IR LOGIN-REFERRALS ID ENABLE IDLE SORT SORT=DISPLAY THREAD=REFERENCES THREAD=REFS THREAD=ORDEREDSUBJECT MULTIAPPEND URL -PARTIAL CATENATE UNSELECT CHILDREN NAMESPACE UIDPLUS LIST-EXTENDED I18NLEVEL=1 CONDSTORE QRESYNC ESEARCH ESORT SEARCHRES WITHIN CONTEXT=SEARCH LIST-STATUS SPEC IAL-USE BINARY MOVE] Logged in B select INBOX * FLAGS (\Answered \Flagged \Deleted \Seen \Draft) * OK [PERMANENTFLAGS (\Answered \Flagged \Deleted \Seen \Draft \*)] Flags permit ted. * 228 EXISTS * 21 RECENT * OK [UNSEEN 208] First unseen. * OK [UIDVALIDITY 1209955743] UIDs valid * OK [UIDNEXT 99272] Predicted next UID * OK [NOMODSEQ] No permanent modsequences B OK [READ-WRITE] Select completed (0.416 secs). C logout * BYE Logging out C OK Logout completed. Connection closed by foreign host. $
In the example above, I entered an incrementing alphabetical character, i.e., "A", "B", "C", before each command. You can enter a word of your choosing before each command. The server will include that word at the beginning of its response, e.g. "C OK Logout completed." If you don't include a word, or letter, preceding the IMAP command, you will see an error message stating "Unknown command" such as shown below:
select inbox select BAD Error in IMAP command INBOX: Unknown command.
The purpose of putting a unique word before each command is to allow the client to asociate each response with the corresponding command issued by the client. A client program might issue several commands without waiting for a response, so when it gets the reponses it can associate each one with the corresponding command it issued. E.g., I could also have used "a1", "a2", "a3", etc. as in the example below:
$ telnet localhost 143 Trying ::1... Connected to localhost. Escape character is '^]'. * OK [CAPABILITY IMAP4rev1 LITERAL+ SASL-IR LOGIN-REFERRALS ID ENABLE IDLE START TLS AUTH=PLAIN] Dovecot ready. a1 login nell ASecretPassword a1 OK [CAPABILITY IMAP4rev1 LITERAL+ SASL-IR LOGIN-REFERRALS ID ENABLE IDLE SORT SORT=DISPLAY THREAD=REFERENCES THREAD=REFS THREAD=ORDEREDSUBJECT MULTIAPPEND UR L-PARTIAL CATENATE UNSELECT CHILDREN NAMESPACE UIDPLUS LIST-EXTENDED I18NLEVEL=1 CONDSTORE QRESYNC ESEARCH ESORT SEARCHRES WITHIN CONTEXT=SEARCH LIST-STATUS SPE CIAL-USE BINARY MOVE] Logged in a2 select inbox * FLAGS (\Answered \Flagged \Deleted \Seen \Draft) * OK [PERMANENTFLAGS (\Answered \Flagged \Deleted \Seen \Draft \*)] Flags permit ted. * 229 EXISTS * 1 RECENT * OK [UNSEEN 208] First unseen. * OK [UIDVALIDITY 1209955743] UIDs valid * OK [UIDNEXT 99273] Predicted next UID * OK [NOMODSEQ] No permanent modsequences a2 OK [READ-WRITE] Select completed (0.028 secs). a3 Examine inbox * OK [CLOSED] Previous mailbox closed. * FLAGS (\Answered \Flagged \Deleted \Seen \Draft) * OK [PERMANENTFLAGS ()] Read-only mailbox. * 229 EXISTS * 0 RECENT * OK [UNSEEN 208] First unseen. * OK [UIDVALIDITY 1209955743] UIDs valid * OK [UIDNEXT 99273] Predicted next UID * OK [NOMODSEQ] No permanent modsequences a3 OK [READ-ONLY] Examine completed (0.028 secs). a4 logout * BYE Logging out a4 OK Logout completed. Connection closed by foreign host. $
In the above example, I used another command, examine which can,
as with the select command, be used to obtain information on a
mailbox on the server for that account.
If you want to retrieve a message from a mailbox, you can use the
FETCH command. E.g., when I issue the select inbox
command in the example below, I can see there are 232 messages in the user's
inbox. I can use fetch 232 body to see information regarding the
last message received or I can use fetch 232 body[] to view the
contents of the last message received, which will show me the entire message.
Or I can use Fetch 232 (BODY.PEEK[HEADER]) to view just the
message header.
$ telnet localhost 143
Trying ::1...
Connected to localhost.
Escape character is '^]'.
* OK [CAPABILITY IMAP4rev1 LITERAL+ SASL-IR LOGIN-REFERRALS ID ENABLE IDLE START
TLS AUTH=PLAIN] Dovecot ready.
A login nell ASecretPassword
A OK [CAPABILITY IMAP4rev1 LITERAL+ SASL-IR LOGIN-REFERRALS ID ENABLE IDLE SORT
SORT=DISPLAY THREAD=REFERENCES THREAD=REFS THREAD=ORDEREDSUBJECT MULTIAPPEND URL
-PARTIAL CATENATE UNSELECT CHILDREN NAMESPACE UIDPLUS LIST-EXTENDED I18NLEVEL=1
CONDSTORE QRESYNC ESEARCH ESORT SEARCHRES WITHIN CONTEXT=SEARCH LIST-STATUS SPEC
IAL-USE BINARY MOVE] Logged in
B select inbox
* FLAGS (\Answered \Flagged \Deleted \Seen \Draft)
* OK [PERMANENTFLAGS (\Answered \Flagged \Deleted \Seen \Draft \*)] Flags permit
ted.
* 232 EXISTS
* 0 RECENT
* OK [UNSEEN 208] First unseen.
* OK [UIDVALIDITY 1209955743] UIDs valid
* OK [UIDNEXT 99276] Predicted next UID
* OK [NOMODSEQ] No permanent modsequences
B OK [READ-WRITE] Select completed (0.028 secs).
C fetch 232 body
* 232 FETCH (BODY ("TEXT" "PLAIN" ("format" "flowed" "charset" "US-ASCII") NIL N
IL "7bit" 17 1))
C OK Fetch completed.
D fetch 232 body[]
* 232 FETCH (FLAGS (\Seen) BODY[] {723}
Return-Path: <root@example.com>
Received: from example.com (localhost [127.0.0.1])
by example.com (8.14.7/8.14.7) with ESMTP id v6SISBnq002954
for <nell@example.com>; Fri, 28 Jul 2017 14:28:11 -0400
Received: from localhost (root@localhost)
by example.com (8.14.7/8.14.7/Submit) with ESMTP id v6SISBmS002950
for <nell@example.com>; Fri, 28 Jul 2017 14:28:11 -0400
Date: Fri, 28 Jul 2017 14:28:11 -0400 (EDT)
From: root <root@example.com>
To: Nell Gwyn <nell@example.com>
Subject: Hello
Message-ID: <alpine.LRH.2.11.1707281427400.2341@example.com>
User-Agent: Alpine 2.11 (LRH 23 2013-08-11)
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; format=flowed; charset=US-ASCII
A test message.
)
D OK Fetch completed.
E Fetch 232 (BODY.PEEK[HEADER])
* 232 FETCH (BODY[HEADER] {706}
Return-Path: <root@example.com>
Received: from example.com (localhost [127.0.0.1])
by example.com (8.14.7/8.14.7) with ESMTP id v6SISBnq002954
for <nell@example.com>; Fri, 28 Jul 2017 14:28:11 -0400
Received: from localhost (root@localhost)
by example.com (8.14.7/8.14.7/Submit) with ESMTP id v6SISBmS002950
for <nell@example.com>; Fri, 28 Jul 2017 14:28:11 -0400
Date: Fri, 28 Jul 2017 14:28:11 -0400 (EDT)
From: root <root@example.com>
To: Nell Gwyn <nell@example.com>
Subject: Hello
Message-ID: <alpine.LRH.2.11.1707281427400.2341@example.com>
User-Agent: Alpine 2.11 (LRH 23 2013-08-11)
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; format=flowed; charset=US-ASCII
)
E OK Fetch completed.
F logout
* BYE Logging out
F OK Logout completed.
Connection closed by foreign host.
$The following flags can be associated with a message:
| \Seen | Message has been read |
| \Answered | Message has been answered |
| \Flagged | Message is "flagged"for urgent/special attention |
| \Deleted | Message is "deleted" for removal by later EXPUNGE |
| \Draft | Message has not completed composition |
| \Recent | Message has arrived since the previous time this mailbox was selected |
You can see the flags on messages using the fetch command. You
can specify a range of messages to check in the form
fetch start_number:end_number. E.g., if the mailbox in the examples
above has 232 messages in it, I can view the flags for messages 200 through 210
with the command fetch 200:210 flags.
C fetch 200:210 FLAGS * 200 FETCH (FLAGS (\Seen)) * 201 FETCH (FLAGS (\Seen)) * 202 FETCH (FLAGS (\Seen)) * 203 FETCH (FLAGS (\Seen)) * 204 FETCH (FLAGS (\Seen)) * 205 FETCH (FLAGS (\Seen)) * 206 FETCH (FLAGS (\Seen)) * 207 FETCH (FLAGS (\Seen)) * 208 FETCH (FLAGS ()) * 209 FETCH (FLAGS ()) * 210 FETCH (FLAGS ()) C OK Fetch completed.
From the output shown above, I can see that messages 200 through 207 have already been seen, but messages that arrived after message number 207 have not yet been seen.
References: