You can usually tell what country someone is in by looking at their email address.
For instance, micky.mouse@ukonline.co.uk is in the United Kingdom. The trick is to look at the last two letter of the email address. They will usually be a fairly obvious abbreviation of the country name
In addition to explicit country codes, it is also helpful to know that ".com", ".net", ".edu", and ".org" are U.S. domains 99% of the time.
This is a list based on the lists of entities contained
in the ISO 3166:1988 standard, Third edition 1988-08-15.
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Codes from ISO 3166 Version: III-58, 1993-08-11
DOMAIN COUNTRY (short name in English)
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.ad ANDORRA
.ae UNITED ARAB EMIRATES
.af AFGHANISTAN
.ag ANTIGUA AND BARBUDA
.ai ANGUILLA
.al ALBANIA
.am ARMENIA
.an NETHERLANDS ANTILLES
.ao ANGOLA
.aq ANTARCTICA
.ar ARGENTINA
.as AMERICAN SAMOA
.at AUSTRIA
.au AUSTRALIA
.aw ARUBA
.az AZERBAIJAN
.ba BOSNIA AND HERZEGOWINA
.bb BARBADOS
.bd BANGLADESH
.be BELGIUM
.bf BURKINA FASO
.bg BULGARIA
.bh BAHRAIN
.bi BURUNDI
.bj BENIN
.bm BERMUDA
.bn BRUNEI DARUSSALAM
.bo BOLIVIA
.br BRAZIL
.bs BAHAMAS
.bt BHUTAN
.bv BOUVET ISLAND
.bw BOTSWANA
.by BELARUS
.bz BELIZE
.ca CANADA
.cc COCOS (KEELING) ISLANDS
.cf CENTRAL AFRICAN REPUBLIC
.cg CONGO
.ch SWITZERLAND
.ci COTE D'IVOIRE
.ck COOK ISLANDS
.cl CHILE
.cm CAMEROON
.cn CHINA
.co COLOMBIA
.com UNITED STATES (generally)
.cr COSTA RICA
.cu CUBA
.cv CAPE VERDE
.cx CHRISTMAS ISLAND
.cy CYPRUS
.cz CZECH REPUBLIC
.de GERMANY
.dj DJIBOUTI
.dk DENMARK
.dm DOMINICA
.do DOMINICAN REPUBLIC
.dz ALGERIA
.ec ECUADOR
.edu UNITED STATES (generally)
.ee ESTONIA
.eg EGYPT
.eh WESTERN SAHARA
.er ERITREA
.es SPAIN
.et ETHIOPIA
.fi FINLAND
.fj FIJI
.fk FALKLAND ISLANDS (MALVINAS)
.fm MICRONESIA (FEDERATED STATES OF)
.fo FAROE ISLANDS
.fr FRANCE
.fx FRANCE, METROPOLITAN
.ga GABON
.gb UNITED KINGDOM
.gd GRENADA
.ge GEORGIA
.gf FRENCH GUIANA
.gh GHANA
.gi GIBRALTAR
.gl GREENLAND
.gm GAMBIA
.gn GUINEA
.gp GUADELOUPE
.gq EQUATORIAL GUINEA
.gr GREECE
.gs SOUTH GEORGIA AND THE SOUTH SANDWICH ISLANDS
.gt GUATEMALA
.gu GUAM
.gw GUINEA-BISSAU
.gy GUYANA
.hk HONG KONG
.hm HEARD AND MC DONALD ISLANDS
.hn HONDURAS
.hr CROATIA
.ht HAITI
.hu HUNGARY
.id INDONESIA
.ie IRELAND
.il ISRAEL
.in INDIA
.io BRITISH INDIAN OCEAN TERRITORY
.iq IRAQ
.ir IRAN (ISLAMIC REPUBLIC OF)
.is ICELAND
.it ITALY
.jm JAMAICA
.jo JORDAN
.jp JAPAN
.ke KENYA
.kg KYRGYZSTAN
.kh CAMBODIA
.ki KIRIBATI
.km COMOROS
.kn SAINT KITTS AND NEVIS
.kp KOREA, DEMOCRATIC PEOPLE'S REPUBLIC OF
.kr KOREA, REPUBLIC OF
.kw KUWAIT
.ky CAYMAN ISLANDS
.kz KAZAKHSTAN
.la LAO PEOPLE'S DEMOCRATIC REPUBLIC
.lb LEBANON
.lc SAINT LUCIA
.li LIECHTENSTEIN
.lk SRI LANKA
.lr LIBERIA
.ls LESOTHO
.lt LITHUANIA
.lu LUXEMBOURG
.lv LATVIA
.ly LIBYAN ARAB JAMAHIRIYA
.ma MOROCCO
.mc MONACO
.md MOLDOVA, REPUBLIC OF
.mg MADAGASCAR
.mh MARSHALL ISLANDS
.mk MACEDONIA, THE FORMER YUGOSLAV REPUBLIC OF
.ml MALI
.mm MYANMAR
.mn MONGOLIA
.mo MACAU
.mp NORTHERN MARIANA ISLANDS
.mq MARTINIQUE
.mr MAURITANIA
.ms MONTSERRAT
.mt MALTA
.mu MAURITIUS
.mv MALDIVES
.mw MALAWI
.mx MEXICO
.my MALAYSIA
.mz MOZAMBIQUE
.na NAMIBIA
.nc NEW CALEDONIA
.ne NIGER
.net UNITED STATES (generally)
.nf NORFOLK ISLAND
.ng NIGERIA
.ni NICARAGUA
.nl NETHERLANDS
.no NORWAY
.np NEPAL
.nr NAURU
.nu NIUE
.nz NEW ZEALAND
.om OMAN
.org UNITED STATES (generally)
.pa PANAMA
.pe PERU
.pf FRENCH POLYNESIA
.pg PAPUA NEW GUINEA
.ph PHILIPPINES
.pk PAKISTAN
.pl POLAND
.pm ST. PIERRE AND MIQUELON
.pn PITCAIRN
.pr PUERTO RICO
.pt PORTUGAL
.pw PALAU
.py PARAGUAY
.qa QATAR
.re REUNION
.ro ROMANIA
.ru RUSSIAN FEDERATION
.rw RWANDA
.sa SAUDI ARABIA
.sb SOLOMON ISLANDS
.sc SEYCHELLES
.sd SUDAN
.se SWEDEN
.sg SINGAPORE
.sh ST. HELENA
.si SLOVENIA
.sj SVALBARD AND JAN MAYEN ISLANDS
.sk SLOVAKIA
.sl SIERRA LEONE
.sm SAN MARINO
.sn SENEGAL
.so SOMALIA
.sr SURINAME
.st SAO TOME AND PRINCIPE
.sv EL SALVADOR
.sy SYRIAN ARAB REPUBLIC
.sz SWAZILAND
.tc TURKS AND CAICOS ISLANDS
.td CHAD
.tf FRENCH SOUTHERN TERRITORIES
.tg TOGO
.th THAILAND
.tj TAJIKISTAN
.tk TOKELAU
.tm TURKMENISTAN
.tn TUNISIA
.to TONGA
.tp EAST TIMOR
.tr TURKEY
.tt TRINIDAD AND TOBAGO
.tv TUVALU
.tw TAIWAN, PROVINCE OF CHINA
.tz TANZANIA, UNITED REPUBLIC OF
.ua UKRAINE
.ug UGANDA
.um UNITED STATES MINOR OUTLYING ISLANDS
.us UNITED STATES
.uy URUGUAY
.uz UZBEKISTAN
.va VATICAN CITY STATE (HOLY SEE)
.vc SAINT VINCENT AND THE GRENADINES
.ve VENEZUELA
.vg VIRGIN ISLANDS (BRITISH)
.vi VIRGIN ISLANDS (U.S.)
.vn VIET NAM
.vu VANUATU
.wf WALLIS AND FUTUNA ISLANDS
.ws SAMOA
.ye YEMEN
.yt MAYOTTE
.yu YUGOSLAVIA
.za SOUTH AFRICA
.zm ZAMBIA
.zr ZAIRE
.zw ZIMBABWE