Post offices are the same all over. Usually slow, and mostly a bit understaffed. However, this…read moreone's staff does their best in its newer location off the plaza near the Mercado.
The staff is friendly, and though none speak English, each time I've visited they have been kind and patient.
Patient is what you'll have to be too, on the occasion of any visit as there will be a wait. I'd suggest avoiding early morning visits as those will tend to produce the longest lines. I've had better luck in early afternoon (between 11:00 and 1:00) but do bear in mind that they close by 2:30 for the day, so don't wait too long or you'll miss your chance completely.