Ottoman Iraq, 1863-1918
Currency: Ottoman piastre (40 paras = 1 piastre)
To compress several centuries of history into a couple sentences, what is now modern-day Iraq fell under Ottoman control in 1533 and, more or less, remained a part of the Empire until the end of the First World War. The administrative sub-divisions changed around on occasion, but in its final configuration (from 1831 onwards) Iraq was divided into three vilayets, each named after their largest city: Basra, Baghdad and Mosul. Baghdad vilayet was approximately twice the size of the other two regions.
A public postal service was established in the Empire in 1840. Iraq was not generously served by it: in 1863, when the Empire's postage stamps were first issued, there were just two post offices in all of Iraq (at Mosul and Baghdad, although letters could apparently be accepted at other unspecified locations). Further offices were opened sporadically.
Strangely I've been unable to actually establish when postage stamps were introduced to Iraq: Proud says 1868 but the stamp at top-left above has a postmark dated 1281 (per the Turkish calendar), which comes out as 1865 or 1866 by my understanding. Anyway stamps appeared at some point in the 1860s, and throughout the whole Ottoman period regular Ottoman stamps were used in Iraq without any differentiation. The only peculiarity specific to Iraq was the authorisation of bisects in 1879 and 1882: on both occasions 2 piastre stamps were cut in half and overprinted to meet a local shortage of 1 piastre stamps. Both of these issues were entirely sincere and done to address a genuine postal need, but of course they didn't escape the notice of collectors and today one can find neat on-piece specimens on Ebay for not a huge amount of money (I don't have one, despite this).
The British had had a commercial presence in Iraq since the 18th Century and by the early 19th Century there was a British consul at Baghdad and a lower-ranking official in/around Basra. Between them they ran a fairly efficient postal operation of their own: a mail ship ran between Bombay and Basra, and mounted messengers were hired to carry post between Basra and Baghdad, and from there to Constantinople through Anatolia, or to the Mediterranean coast via Syria. In 1868 this service was integrated into the Indian civil postal service and from the 1st January of that year regular Indian stamps were used.
The Ottoman post in Iraq was fairly haphazard in its earlier days, and the British post was regarded as a safer, more reliable service. It should of course be noted that the British post was just one of many European postal services operating out of Ottoman territory, although Britain was the only country to have a service in Iraq (the other European posts generally being in Constantinople and the Levant). The Ottomans, presumably recognising the deficiencies of their own service, were initially tolerant of the European ones.
The Ottoman post however cleaned up its act somewhat and was admitted to the Universal Postal Union in 1875. Regarding their admission to the Postal Union as international validation of the quality of their own service, the Ottoman government began to demand the removal of the foreign posts. Attempts were made to, variously, hinder the operation of the British post and to compete with it, but (to cut a long story short) the British offices remained open.
By 1914 there seems to have been around fifty Ottoman post offices in Iraq (per Gibbons), together with the two British offices. The First World War broke out in July 1914 and, while the Ottoman Empire was initially neutral, its sympathies were clearly leaning towards the Central Powers. With tensions rising, the British post offices in Iraq were closed down on the 30th September. Britain declared war on the Ottoman Empire on the 5th November and immediately went on the offensive: on 22nd November Basra was captured by the Indian Expeditionary Force and the post office was re-opened by the end of the month.
The British immediately began to push up in the direction of Baghdad. The Indian Expeditionary Force had its own system of field post offices (outside the scope of this website, for the time being) and used Indian stamps overprinted with "I.E.F.". Civil post offices were gradually opened in British-controlled territory for non-military use: these seem to have been run by seconded Indian officials together with local assistants.
I unfortunately know very little about the operation of the Ottoman posts in Iraq during the First World War: presumably services continued to function in some sort of restricted condition.
By late 1915 the British had advanced to within 30 miles of Baghdad, but were checked by the Ottomans at the Battle of Ctesiphon. They retreated to Kut-al-Amara and were besieged there. Attempts to relieve the British defenders were beaten back by the Ottomans and, ravaged by disease and running out of supplies, the British surrendered on the 29th April 1916. Over 13,000 British and Indian soldiers were taken prisoner in one of the worst defeats for the British during the war. And we leave the British story here for now.
 I use "Iraq" throughout this page and the next few as an abbreviation for "the territory which is presently known as Iraq" - the term is an anachronism for the Ottoman period. During this time the area was generally known to English-speakers as Mesopotamia (or "Turkish Arabia", occasionally). "Irak" seems to have had some currency in French.
 Proud explores this in as much detail as anybody might wish: the main points of contention —beyond the bare fact that the British offices existed— were the Ottoman belief that that the Baghdad office was failing to pay customs duties on packages it received from India, and that the Basra office had erected a pillar-box some distance away from its actual premises.
 I use the passive voice here deliberately: I recall reading somewhere that the British offices were ordered closed by the Ottomans, instead of the British sensing war on the horizon and closing the offices as a precaution, but I now cannot locate where I read this.