Try a field constructed as:
{IF«Contacts_Client_Mortgagee_MAILING_ADD1»= "" «Contacts_Client_Mortgagee_MAILING_ADD» "«Contacts_Client_Mortgagee_MAILING_ADD»↵
{IF«Contacts_Client_Mortgagee_MAILING_ADD2»= "" «Contacts_Client_Mortgagee_MAILING_ADD1» "«Contacts_Client_Mortgagee_MAILING_ADD1»↵
{IF«Contacts_Client_Mortgagee_MAILING_ADD3»= "" «Contacts_Client_Mortgagee_MAILING_ADD2» "«Contacts_Client_Mortgagee_MAILING_ADD2»↵
«Contacts_Client_Mortgagee_MAILING_ADD3»"}"}"}

Note: The field brace pairs (i.e. '{ }') for the above example are all created in the document itself, via Ctrl-F9 (Cmd-F9 on a Mac or, if you’re using a laptop, you might need to use Ctrl-Fn-F9); you can't simply type them or copy & paste them from this message. Nor is it practical to add them via any of the standard Word dialogues. Likewise, the chevrons (i.e. '« »') are part of the actual mergefields - which you can insert from the 'Insert Merge Field' dropdown (i.e. you can't type or copy & paste them from this message, either). The spaces represented in the field constructions are all required. Instead of the ↵ symbols, you should use real line/paragraph breaks.

__________________
Cheers,
Paul Edstein
[Fmr MS MVP - Word]