If by 'send it in the same format as it appears in Word', you mean the message body should have the same format, then you are destined to be disappointed. Word document format and html e-mail format are entirely different from one another. You can get it close if you start by formatting the document in Word's web view, but an exact facsimile is unrealistic.
If format is important then mail it as an attachment in PDF format.
http://www.gmayor.com/ManyToOne.htm in one to one mode will achieve either a formatted merge to e-mail body or as an attachment (with or without a personalised covering message). The only proviso is that the merge data must be an Excel worksheet (with the e-mail addresses in the records). The BCC is also possible.
Having said that, it is possible to improve on your macro, but there are some anomalies e.g. you have both the Source Document and the Maillist Document set as the activedocument, which seems odd, given that Source is presumably the product of a mail merge to a new document. You will have to explain that one.
Rather than just use the .Body of the message, you need to use the Outlook Inspector to enable you to edit the message body e.g. something along the lines of
Code:
For j = 1 To Source.Sections.Count - 1
Set oItem = oOutlookApp.CreateItem(olMailItem)
With oItem
.BodyFormat = 2
Set olInsp = .GetInspector
Set wdDoc = olInsp.WordEditor
Set oRng = wdDoc.Range
'If you don't want the default signature, remove the next line
oRng.Collapse 1
.Display 'this must not be removed.
.Subject = mysubject
oRng.FormattedText = Source.Sections(j).Range.FormattedText
Set Datarange = Maillist.Tables(1).Cell(j, 1).Range
Datarange.End = Datarange.End - 1
.to = Datarange
.BCC = "amentinho@example.com"
For i = 2 To Maillist.Tables(1).Columns.Count
Set Datarange = Maillist.Tables(1).Cell(j, i).Range
Datarange.End = Datarange.End - 1
.Attachments.Add Trim(Datarange.Text), olByValue, 1
Next i
.Send
End With
Set oItem = Nothing
Next j
is probably not far off (olInsp, wdDoc and oRng are each declared as Object) but without the document to test against it is only a guide.