From time to time, you will find yourself having to communicate with your tenant formally during a tenancy.  This is done by way of serving your tenant a notice/document (which is really legal talk for someone to legally receive your communication and be notified of its contents).  
Be it a 14-day notice to remedy, a rent increase letter, or even a notice to terminate, sections 136 and 136A of the Residential Tenancies Act set out the legal parameters within which notices can be served on a tenant.  
Here is a break-down of rules and timeframes:
Types of service Methods 
 The day on which notice takes effect* If served on a Monday, notice is deemed to legally commence on
In person Physically handing the notice to the tenant. If the recipient refuses to accept, than dropping it at their feet.   The following day
 Tuesday 
By post  Posting the document to the address for service provided (best to retain tracking details). 4 working days after the date of posting  Friday
By delivery To the address of the tenancy:
  • placing the notice in the mailbox;
  • attaching notice to the door in a prominent position; 
  • handing it to a person who appears to be over 16 and who resides at the premises.
To any other place of residence...