eceipt/Acknowledgement of Naturalisation Application

When an application is made for Naturalisation as an Irish Citizen what does the receipt/acknowledgement of application say? And is it a posted letter?

We are looking to travel soon an want to avoid issue returning to Dublin. As we live in N. Ireland my wife has a family permit (due to expire soon) via the British immigration system, so she doesn't receive any stamps the way applicants may receive in Ireland.

Also, from other topics it looks like people are waiting a while for these responses!

Many thanks