If you wish to send a mail from an another email account, you can add the account name to SentOnBehalfOfName property of your mail object.
Note : Sometimes, the mailboxes takes time to respond, so I added a while loop to make sure that its' been added. You may add a counter or time variable to exit from the while loop if your mailbox is taking too long to respond, so you will not end up in a infinite loop.
Dim OutMail As Object, Cell As Range, OutApp As Object
Set OutApp = CreateObject("Outlook.Application")
Set OutMail = OutApp.CreateItem(0)
.To = "firstname.lastname@example.org"
.CC = "email@example.com"
'.BCC = "firstname.lastname@example.org"
.Subject = "subject"
'check errors & timing
On Error Resume Next
.SentOnBehalfOfName = "Sendfrom@gmail.com"
Do While Err.Number <> 0
.SentOnBehalfOfName = MailBody.Range("B3")
On Error GoTo 0
.HTMLBody = "this is body"