I was under the understanding they could be mailed with the TO's permission. I'll give it a few days and if no Irish Geocacher offers an address, I'll move it a bit closer to the west coast.
Thank you for the advise.
The Groundspeak guide says:
3.4. Mailing Trackables to Another Geocacher
There may be occasions when you want to mail a Trackable to a geocacher in another location. Please do not mail any trackable without asking the owner first. Mail services to some places are erratic and/or unreliable. Typically, Trackables should travel from geocache to geocache, or directly from the hands of one geocacher to another.
If you have received a Trackable in the mail, you will want to post a "grab it" logtype rather than "retrieve it" logtype, since you're not retrieving it directly from a geocache. The mileage traveled will show the next time you drop it in a geocache.