This worked here; replace your .body = line with
.htmlBODY = "Dear <STRONG>" & StrConv(Left(Cells(cell.Row, "A"), InStr(1, Cells(cell.Row, "A"), ".") - 1), 3) & "</STRONG>," _
& "<p>" & "<p>" & "Please contact us to discuss bringing your account up to date"
2018-01-21_174949.jpg
You say you want to use it several times in the message, so perhaps something like:
.htmlBODY = "Dear " & BoldName & "," & "<p>" & "<p>" & "Please contact us to discuss bringing your account in the name of " & BoldName & " up to date"
or a bit shorter:
.htmlBODY = "Dear " & BoldName & ",<p><p>Please contact us to discuss bringing your account in the name of " & BoldName & " up to date"
where beforehand you've set up the variable BoldName like:
BoldName = "<STRONG>" & StrConv(Left(Cells(cell.Row, "A"), InStr(1, Cells(cell.Row, "A"), ".") - 1), 3) & "</STRONG>"
2018-01-21_175712.jpg