Protecting the POP3 Password with APOP
Traditional POP3 servers expect to receive the account password
in plain text format. The problem with plain text format is
that it can easily be intercepted by hackers, giving them complete
access to your POP3 account. An extension to POP3, titled
APOP, has been developed as a countermeasure. With APOP
authentication, the password is never sent across the network.
This is great, but you may be asking, "How can the server
authenticate a user if the password is never sent across the
network?"
The answer is that the client application creates a digest that is
computed from the password
and the current time. The client application sends the
digest to the server in-lieu-of the password. The server performs the same
calculation to create its own digest and then compares it to the
digest it received from the client. If the two digests match,
the user is authenticated. Since the digest is computed from
the current time, it changes with every login. If it is intercepted by a hacker, it is useless because it will no
longer be valid, since the time has changed. The internals
of this authentication are quite complex and I will not go into
them here. The
EasyMail
POP3 object makes APOP
authentication very easy and handles all the complexities for you.
set objPOP3 = CreateObject("EasyMail.POP3")
objPOP3.MailServer="mail.domain.com"
objPOP3.Account="account"
objPOP3.Password="password"
objPOP3.AuthMode=256+16
objPOP3.Connect
cnt = objPOP3.GetDownloadableCount()
MsgBox cnt & " messages available."
objPOP3.Disconnect
By setting the AuthMode property to 256, we enable APOP
authentication. Since APOP is an extension to POP3, it is
not supported by all POP3 servers. By adding 16 to the
AuthMode property we instruct the
EasyMail
POP3 object to automatically downgrade to plain text authentication if the server does not
support APOP. This enables our application to use APOP if
available, and automatically use conventional POP3 authentication if APOP is not
supported by the server.
Downloading Messages
In this example, we will download and parse every message
in the mailbox. When the operation is complete, we will use
a message box to display the subject of the first message.
We will not display the subject of every message, to keep things
simple. A word
of caution: Since this code downloads every message in the
mailbox, it may take a long time to execute if the mailbox
contains many messages. It is often more efficient to
download messages in small groups as the next sample will
demonstrate, however some applications will benefit from
downloading all messages at once because they will not be dealing with large mailboxes, and
the code is very easy and straight forward:
set objPOP3 = CreateObject("EasyMail.POP3")
objPOP3.MailServer="mail.domain.com"
objPOP3.Account="account"
objPOP3.Password="password"
objPOP3.Connect
objPOP3.DownloadMessages(0)
MsgBox "Subject: " & objPOP3.Messages(1).Subject
objPOP3.Disconnect
The zero parameter to DownloadMessages() instructs the
EasyMail
POP3 object not to mark the message for deletion after downloading.
The DownloadMessages() method automatically parses the downloaded
messages and exposes the data via the Messages collection.
More on message deletion and parsing later...
A More Efficient Download
Efficient POP3 applications download message headers first, and
do not download the complete message unless the user specifically
requests it. The message headers contain dates and
addressing information plus the subject, and this is enough to
build a table or list box to display the messages to the user. When the
user selects a specific message to view, you can download the
entire message and display the contents. This approach saves time and
bandwidth. Also, as mentioned in the previous example, it is
often more efficient to download messages in small batches rather
than downloading every message in one pass. This type of
efficiency becomes more important with larger mailboxes and/or
slower connections to the server.
set objPOP3 = CreateObject("EasyMail.POP3")
objPOP3.MailServer="mail.domain.com"
objPOP3.Account="account"
objPOP3.Password="password"
objPOP3.Connect
'download first 5 headers and
'display their subjects
nMsgCount=objPOP3.GetDownloadableCount()
nLastMessage = 5
if nLastMessage > nMsgCount then
nLastMessage = nMsgCount
end if
for x = 1 to nLastMessage
objPOP3.DownloadSingleMessageHeaders(x)
MsgBox objPOP3.Messages(x).Subject
next
'download full message from first header
'and display attachment count
if objPOP3.Messages.Count then
nFullMsg=objPOP3.DownloadSingleMessage(1)
nCnt=objPOP3.Messages(nFullMsg).Attachments.Count
MsgBox "Attachment count: " & nCnt
objPOP3.Messages.Delete(nFullMsg)
end if
objPOP3.Disconnect
This sample downloads the first 5 messages on the server, or
every message if there are 5 or less. The execution speed of
this sample should be very fast, unless you have a slow connection
to the server. Finally, we simulate the user selecting the
first message in the list and download it in its entirety.
We can then display the attachment count.
This code can easily be expanded and adapted to provide paging
capabilities in your application. Enabling your application
to display multiple pages of 10-20 messages each will increase its
speed and decrease its resource consumption.
Up next: How to parse downloaded messages and access
their parts including attachments, HTML and more...
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