You can alter your data source (query) to add a new field or just add a text box and apply to the control source property.
Query Field: MailingAddres1and2: IIf(IsNull(MailingAddress1), MailingAddress, MailingAddress & Chr(10) & MailingAddress)
or Control Source of a Text box: =IIf(IsNull(MailingAddress1), MailingAddress, MailingAddress & Chr(10) & MailingAddress)
Chr(10) will insert a carriage return.