The Russian postal service is Pochta Rossia (www.pochta.ru). Pochta (ПОЧТАМТ) refers to any post office, glavpochtamt to a main post office and mezhdunarodny glavpochtamt to an international one.
Outward post is slow but fairly reliable; if you want to be certain, use registered post (zakaznaya pochta). Airmail letters take two to three weeks from Moscow and St Petersburg to the UK, longer from other cities and three to four weeks to the US or Australasia. To send a postcard or letter up to 20g anywhere in the world by air costs R37.
In major cities you can usually find the services of at least one of the international express carriers, such as FedEx or DHL.
Incoming mail is so unreliable that many companies, hotels and individuals use private services with addresses in Germany or Finland (a private carrier completes the mail’s journey to its Russian destination). Other than this, your reliable options for receiving mail in Russia are nil: there’s no poste restante, and embassies and consulates won’t hold mail for transient visitors.
If sending mail to Russia or trying to receive it, note that addresses should be in reverse order: Russia (Россия), postal code (if known), city, street address, then name.