Android Tutorial Using POP3 to communicate with Android devices

Many developers face the challenge of sending data to remote devices. These devices can be at times offline, sleeping or without proper network coverage.
There are several possible solutions. The device can contact a web server which will return the required data.
Another solution is to use Google push notification framework.
Here I want to present a third solution which doesn't require any custom server and is pretty simple.
Using the Net library a device can connect to a mail server and download the mail messages.
This solution can fit very well in many cases and is very simple to manage. Mail servers are very common and are easy to work with.
All you need is an email service that supports POP3. Gmail is one such service.

The POP3 object from the Net library returns the raw messages as strings.
Additional work is required to get the message fields and especially to extract attachments from the messages.
MailParser code module is included in the attached project.
MailParser parses the messages, saves the attachments and returns Messages objects which hold the various fields.

MailParser cannot be used as a real mail client. There are many possible formats and encodings. MailParser can handle simple formats with zero or more attachments.

Parsing a message is done by calling:

      Dim m As Message
      m = MailParser.ParseMail(MessageText, File.DirRootExternal)

The first parameter is the raw message and the second is the folder that the attachments will be saved to.

MailParser requires StringUtils library for the base64 decoding.

 

[Erel]

Make sure that you are looking at the correct mail. SMTP sets the content type header to: multipart/mixed; bounary... when there is an attachment.

 

[luke2012]

I checked :

The mail contains an attachement and the "Headers" and "Msg" have the following content :

---------------------------------------------------------------------------
<!>anywheresoftware.b4a.keywords.Common 151<!> Headers = Content-Type: text/plain; charset="utf-8"
<!>anywheresoftware.b4a.keywords.Common 151<!> Msg = [Attachments=(ArrayList) [], BCCField=, Body=
, CCField= , ContentType= multipart/mixed; boundary="asdasdwdwqd__HV_qwdqwdddwq", FromField= Risto Lite <luca.colombo75@gmail.com>
, ToField= risto.test2013@gmail.com, Subject= Risto_03/16/2013, IsInitialized=true
--------------------------------------------------------------------------

You can see that the Content-Type in the Headers is different from the Content-Type in the Msg.
The HandlePart sub check for the Content-Type in the "Headers" and fail to download the attachment.

I don't known why...

 

[Erel]

The header should be multipart/mixed. Have you modified the code of MailParser?

Try to send the mail to a client that allows you to see the raw headers.

 

[vukanilod]

Hi,

I'm having problems runing this pop example. it seemed to be working one year ago, and now there is only blank screen... Sorry for reopening the subject, but it is quite strange...

 

[Erel]

Did you check the logs?

 

[zekigultekin]

how can i solve thiss
when i writing edittext.text=m.FromField
it came like this =?iso-8859-1?q?emailadress?=<emailadress@test.com>.
i want to only mail adress. helpp me

 

[Erel]

Which version of Net library are you using?

 

[zekigultekin]

my net lib version is 1.20

 

[Erel]

You will need to manually parse this string:

Sub Activity_Create(FirstTime As Boolean)
   Dim s As String = "=?iso-8859-1?q?emailadress?=<emailadress@test.com>"
   Log (FindEmail(s))
End Sub
Sub FindEmail(s As String) As String
   Dim m As Matcher = Regex.Matcher("<([^>]*)>", s)
   If m.Find Then
      Return m.Group(1)
   Else
      Return ""
   End If
End Sub

 

[zekigultekin]

thank u Erel

 

[caspali]

Sorry erel. How i can check new email arrive on pop in background with a notification?

 

[Erel]

You will need to use a service that periodically checks for new mails. See the services tutorial.

 

[BudiWang]

Hi Erel can u add function to get date time the server mail received the email (not based on phone time)

 

[Erel]

If this value is sent in the headers then it should be quite simple to add it to ParseHeaders sub.

 

[BudiWang]

Have it on Header

example

Received: from mailer01.example.net (mailer01.example.net [192.168.01])
by ixde-df8.example.com (Internet Inbound) with ESMTP id 44524380000AA
for <recipient@example.com>; Sat, 24 Nov 2035 11:45:15 −0500 (EST)

on the last line on received header

can u add to your mailparser function

thanks

 

[Erel]

Look for the Date header. It should look like:
Date: ...

 

[BudiWang]

ok thanks Erel

 

[ComposerB4A]

Hello to all, i search send directly a email (without user intervention), i try:

SMTP.Initialize("smtp.mail.yahoo.com", 465, "email123@yahoo.es","clave123","SMTP")
SMTP.To.Add("email123@yahoo.es")
SMTP.Subject = "hola"
SMTP.Body = "Hola"
SMTP.Send
...
MessageSent event not run

the question, ¿because not send the email?

 

[Erel]

Please start a new thread for this question.

 

[Beja]

Hi Erel,

Today I run the pop3 example.. I can only see a blank screen with the title: POP3 Example.
Any help appreciated.

thanks in advance.