Android Tutorial Using POP3 to communicate with Android devices

Erel · Sep 5, 2011

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:

B4X:

      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 · Apr 10, 2014

Check the logs. It parses the incoming mails and prints them.

Beja · Apr 10, 2014

Hi Erel,
The log says:
java.net.UnknownHostException: myemail@gmail.com

Beja · Apr 10, 2014

also tried pop.gmail.com and got this:
java.net.UnknownHostException: pop.gmail.com

Erel · Apr 11, 2014

Make sure that there is a working internet connection. Test it on a real device.

Beja · Apr 18, 2014

Thanks Erel,
In fact I use real device except in rare cases when I use the emulator..
Any other suggestion appreciated.

Erel · Apr 19, 2014

Are you sure that the device is connected to the internet? This error means that the device wasn't able to resolve the address name and find the IP address.

Beja · Apr 19, 2014

Hi Erel,
This is the only line I modified:
pop.Initialize("pop.google.com", 995, "user@example.com", "password", "pop")

I could use the Internet for all other purposes.

Erel · Apr 21, 2014

Can you post the full error message from the logs?

IslamQabel · May 10, 2014

Hi Erel:
Unfortunately, i receive the following error message
*** Remote compilation mode ***
Parsing code. 0.02
Compiling code. 0.02
Compiling layouts code. 0.00
Sending data to remote compiler. Error
step: Compiling generated Java code.
javac 1.7.0_09
src\anywheresoftware\b4a\samples\pop3\main.java:267: error: package anywheresoftware.b4a.net does not exist
public static anywheresoftware.b4a.net.POPWrapper _pop = null;
^
1 error

Erel · May 11, 2014

You are using the trial version in remote compilation mode. It doesn't support additional libraries. You should use the full version.

IslamQabel · May 12, 2014

Dear All......I am using a program that you can send email using SMTP ......The user have to enter the password in text box, so i want to display the entered password as **************** to hide what written how to do it???

Thanks

IslamQabel · May 12, 2014

You are right Erel.......When using the full version, no problem found

Erel · May 12, 2014

Please start a new thread about the password question.

tactic1960 · Jul 15, 2015

Hi Erel, i used MailParser for save an attachment by i have then same problem of Luke2012. I send the mail with SMTP perfectly, receive the same mail with POP3 but MailParser don't save the file.
I have debugged MailParser and i have see the problem,the function ParseMultipartBody fails.
I attach a file with the mail, if you debug can see the problem

Thanks

Erel · Jul 15, 2015

It misses the closing boundary.
Change ParseMultiparyBody to:

B4X:

Sub ParseMultipartBody (Mail As String, Msg As Message)
   'find first boundary
   index = Mail.IndexOf2("--" & boundary, index)
   ReadNextLine(Mail)
   Dim headers As StringBuilder
   headers.Initialize
   Do While index < Mail.Length
     Dim line As String
     line = ReadNextLine(Mail)
     If line.Length > 0 Then
       headers.Append(line).Append(" ")
     Else If index < Mail.Length Then
       Dim nextPart As Int
       nextPart = Mail.IndexOf2("--" & boundary, index)
       If nextPart = -1 Then nextPart = Mail.Length + 4 '<-- new line
       If nextPart-4 > index Then
         HandlePart(headers.ToString, Mail.SubString2(index, nextPart-4), Msg)
       End If
       index = nextPart
       ReadNextLine(Mail)
       headers.Initialize
     End If
   Loop
End Sub

tactic1960 · Jul 15, 2015

Hi Erel, now ParseMultiparyBody works fine.....

Thank you very much from Italy

le_toubib · Oct 28, 2015

hi all
i m trying this method to communicate with other devices, using gmail, but the error log says i need to web login first ,
indeed i dont to give the username n password to my users to login (that wouldnt even work new gmail security restrictions)
my questions : what are the other free email servers that can work seemlessly with the good old username and password method) using net library without user interference

Erel · Oct 29, 2015

Have you enabled this option: https://www.google.com/settings/security/lesssecureapps ?

le_toubib · Oct 29, 2015

Yes, and enabled pop3 from gmail settings ... Smtp works fine (with security alerts ask the time) but Pop3 requires web login first then it works

le_toubib · Oct 29, 2015

I tried yandex for that purpose , it worked after enabling pop3 without requiring web login

Android Tutorial Using POP3 to communicate with Android devices

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