For more than 11 years now, I opened a postal box, and I've found a service company who open it every week and keep the mail..
When I have a foreseen fixed address (often use American Express offices) I send them an E.mail and they send me the mail..
They can also send me magazines, chart or spare parts when I need them.. (at extra costs)
We used post restante with reasonable success, but in countries where the postal staff don't speak [or read] English, you have to take care.
Mail is filed alphabetically, and a letter addressed to Mr. John Smith can be found filed under 'M', 'J', or 'S' ! We found the answer was to use only surnames, [ the above example would be just Smith ] and not to mention the boats name, for the same reason. This also means that, if you are married, either partner can go for the mail without a jobsworth deciding you can't have it , 'cos you aren't a Mr/Mrs.
They still misfile things, even then, and another weapon is to give whichever friend or relative is going to forward your mail a supply of brightly coloured envelopes to use. They will weed the junk out, and put the rest into one package. If it is misfiled, and the clerk says there's nothing for you, perhaps you will spot 'your' coloured envelope, and direct him/her to it.
With only one package expected, you are free to leave as soon as you have it.
If you are on a tight timetable, then maildrops have to be set up in advance, but if you are staying for a while, the best way is to arrive somewhere, ask those already there what they are doing for mail, and then give the address to whoever is sending it, by telephone, ssb link, e-mail or snail mail. Sometimes a harbourmaster, hotel, bar [Peter Cafe Sport, in Horta, for example] or boatyard is better than Poste Restante.
I suppose it depends which countries you are heading for, but this is hard earned advice for third world places.
