The problem: you have several POP3 accounts and want to combine them into one mailbox and have the email accessible on your smartphone and other computers.

The solution: Use Gmail to collect the email from your accounts.

This works great, as long as you use the Gmail web interface as you can configure Gmail to reply from the address the message was sent to. If you want to download the mail into Outlook, Outlook is going to reply using the gmail address, because it replies using the account that downloaded the message.

Fortunately, Gmail lets you send mail using the connected addresses, even when you use Outlook to send the email. You need to have Gmail configured to send using the account in Settings, Accounts and Import.

Note: These steps may work with any account that lets you collect mail from other server and send mail using any address. It won’t work with Outlook.com at this time, unless the additional addresses are in Microsoft's domains (outlook.com, Hotmail, MSN, etc).

If you want to set a specific account as the default address, enter it in the Account Settings dialog. Replace the name and email address at the top of the dialog with the address you want to have set as default. If you use one of your addresses here, you won't need to add the address to the macros.

To send using one of the other accounts Gmail is collecting mail from, you can select the From > Other Email Address command and type the address in the Send From Other Email Address dialog.
The message header will contain the gmail address, but it won’t be exposed in Outlook.

Return-Path:
Received: from MyHP (my-ip)
by mx.google.com with ESMTPSA id v37sm4082638qge.29.2014.10.24.06.31.34
for
(version=TLSv1 cipher=ECDHE-RSA-AES128-SHA bits=128/128);
Fri, 24 Oct 2014 06:31:34 -0700 (PDT)
From:
To:

Set up the Gmail Account to Send and Receive Your Other EMail Accounts

In Gmail, go to Settings, then Accounts and Import and Add your accounts to the Send mail from section.

In Outlook, use auto account setup to add the Gmail account to your profile. If your POP3 accounts are in your profile (and also configured as an account you can send from in Gmail), you can remove them from Outlook's Email tab in File, Account Settings.

To send a message using one of the POP3 accounts in Gmail:

1. Open a new message.
2. Click From and select Other Email Address.
   

   Note: If you previously used the address, it’s listed in the section above Other Email Address. Select it and return to the message form.

3. Type your POP3 address in the Send From Other Address dialog then click OK to return to the message form.
   
4. The selected address is listed next to the From field.
   

As easy as that is to do, you can use a macro to automate the process. You can also use a macro to open a new message using a specific address and to check the address on outgoing messages.

This will not work with Outlook 2013's "inline replies". Replies and Forwards will be opened in a new Window.

Reply from the address a message was sent to

The following code checks for your specified email addresses in the To/CC field. If it finds one of your addresses, it inserts it in the From field of the reply, the same as if you had used From > Other Email Address field and typed the address in the Send From Other Email Address dialog.

If one of your addresses is not on the recipient list, the reply will be from the default address.

This macro works with Gmail accounts. It does not work with Outlook.com accounts at this time.

This set of macros goes into the ThisOutlookSession module. It runs when Outlook starts and watches for the Reply, ReplyAll, and Forward buttons to be clicked. you can kick start it during testing by clicking in the Startup macro then clicking Run.

Option Explicit
Private WithEvents oExpl As Explorer
Private WithEvents oItem As MailItem
Dim oResponse As MailItem
Dim myAddy As String

Private bDiscardEvents As Boolean
 
 
Private Sub Application_Startup()
   Set oExpl = Application.ActiveExplorer
   bDiscardEvents = False
End Sub
 
Private Sub oExpl_SelectionChange()
   On Error Resume Next
   Set oItem = oExpl.Selection.Item(1)
End Sub
 
' Reply
Private Sub oItem_Reply(ByVal Response As Object, Cancel As Boolean)
   Cancel = True
   bDiscardEvents = True

Set oResponse = oItem.Reply

'run the afterReply macro
 afterReply
'clear myAddy variable
 myAddy = ""

End Sub

Private Sub oItem_Forward(ByVal Response As Object, Cancel As Boolean)
   Cancel = True
   bDiscardEvents = True

Set oResponse = oItem.Forward

'run the afterReply macro
 afterReply
'clear myAddy variable
 myAddy = ""

End Sub

Private Sub oItem_ReplyAll(ByVal Response As Object, Cancel As Boolean)
   Cancel = True
   bDiscardEvents = True

Set oResponse = oItem.ReplyAll

'run the afterReply macro
 afterReply
'remove your address from reply all
 RemoveRecipients oResponse
'clear myAddy variable
 myAddy = ""

End Sub

Private Sub afterReply()

Dim Recipient As Outlook.Recipient
Dim strRecip As String
   
 ' get a list of recipients
For Each Recipient In oItem.Recipients
 strRecip = Recipient.Address & ";" & strRecip
Next Recipient

'check the list for your addresses
'add more elseif lines as needed
If InStr(strRecip, "bcm@outlookbcm.com") > 0 Then
  myAddy = "bcm@outlookbcm.com"
  
  ElseIf InStr(strRecip, "granny@domain.com") > 0 Then
  myAddy = "granny@mobilegranny.com"
  
  ElseIf InStr(strRecip, "alias@msn.com") > 0 Then
  myAddy = "alias@msn.com"

End If

' set the address as the from address
  oResponse.SentOnBehalfOfName = myAddy
  oResponse.Display

End Sub
 

' remove your address from reply all
Private Sub RemoveRecipients(Item As Outlook.MailItem)
  Dim RemoveThis As VBA.Collection
  Dim Recipients As Outlook.Recipients
  Dim R As Outlook.Recipient
  Dim i&, y&
  Set RemoveThis = New VBA.Collection

  RemoveThis.Add myAddy

  Set Recipients = Item.Recipients
  For i = Recipients.Count To 1 Step -1
    Set R = Recipients.Item(i)

    For y = 1 To RemoveThis.Count
      If LCase$(R.Address) = LCase$(RemoveThis(y)) Then
        Recipients.Remove i
        Exit For
      End If
    Next
  Next
End Sub

' check the from on new messages before sending
Private Sub Application_ItemSend(ByVal Item As Object, Cancel As Boolean)
 Dim prompt As String
 Dim strAddress As String
 
On Error Resume Next
 
  If Item.SentOnBehalfOfName <> "" Then
   strAddress = Item.SentOnBehalfOfName
   Else
   strAddress = Item.SendUsingAccount
   End If
If Not Left(LCase(Item.Subject), 3) = "re:" And Not Left(LCase(Item.Subject), 3) = "fw:" Then

      prompt$ = "You sending this from " & strAddress & ". Are you sure you want to send it?"
       If MsgBox(prompt$, vbYesNo + vbQuestion + vbMsgBoxSetForeground, "Check Sending Account") = vbNo Then
         Cancel = True
       End If
End If
 
End Sub

Reply Using the Correct Account Video Tutorial

New Messages using a specific address

To use this code, right click on Project1 and choose Insert > Module. Paste it in the module and update the addresses. If you need more than 3 addresses, duplicate one of the account subs, then change the sub name to something unique (like your email alias or domain name) and replace the email address.

To use, you need to create button on the ribbon for each account sub then click the button when you want to send a new message from a specific account.

Public strFromAddress As String

' Account macros go here
Public Sub mobilegranny()
strFromAddress = "granny@mobilegranny.com"
SendMessageFrom
End Sub

Public Sub outlookbcm()
strFromAddress = "bcm@outlookbcm.com"
SendMessageFrom
End Sub

' Main macro; do not edit
Private Sub SendMessageFrom()
Dim oMail As Outlook.MailItem
 
Set oMail = Application.CreateItem(olMailItem)
    oMail.SentOnBehalfOfName = strFromAddress
    oMail.Display
       
Set oMail = Nothing
 
End Sub

New Messages Using a Specific Address Video Tutorial

How to use macros

First: You need to have macro security set to low during testing. The macros will not work otherwise.

To check your macro security in Outlook 2010 or 2013, go to File, Options, Trust Center and open Trust Center Settings, and change the Macro Settings. In Outlook 2007 and older, it’s at Tools, Macro Security.

After you test the macro and see that it works, you can either leave macro security set to low or sign the macro.

Some macros need to be in ThisOutlookSession, others go into a module or can be placed in either ThisOutlookSession or a module. The instructions are below.

Open the VBA Editor by pressing Alt+F11 on your keyboard.

If you are told to put the code in a module:

1. Right click on Project1 and choose Insert > Module
2. Copy and paste the macro into the new module.

If you are told to put the macro code in ThisOutlookSession:

1. Expand Project1 and double click on ThisOutlookSession.
2. Copy then paste the macro into ThisOutlookSession. (Click within the code, Select All using Ctrl+A, Ctrl+C to copy, Ctrl+V to paste.)

More information as well as screenshots are at How to use the VBA Editor