{"id":289,"date":"2020-04-05T23:29:50","date_gmt":"2020-04-05T21:29:50","guid":{"rendered":"http:\/\/tech.sosthe.sk\/?p=289"},"modified":"2020-04-06T16:30:22","modified_gmt":"2020-04-06T14:30:22","slug":"2-5-aplikacny-protokol-smtp","status":"publish","type":"post","link":"http:\/\/tech.sosthe.sk\/index.php\/2020\/04\/05\/2-5-aplikacny-protokol-smtp\/","title":{"rendered":"2.5.\u2002Aplika\u010dn\u00fd protokol SMTP"},"content":{"rendered":"<p><strong>SMTP: simple mail transfer protocol<\/strong>,\u00a0<a href=\"http:\/\/www.ietf.org\/rfc\/rfc2821.txt\">RFC 2821<\/a><\/p>\n<p>SMTP protokol je ur\u010den\u00fd na odosielanie mailu od pou\u017e\u00edvate\u013ea k svojmu mailov\u00e9mu serveru a na odosielanie mailov od odosielate\u013eovho mailov\u00e9ho servera k mailov\u00e9mu serveru pr\u00edjemcu. SMTP servery po\u010d\u00favaj\u00fa na porte 25.<\/p>\n<p>SMTP protokol je ve\u013emi star\u00fd. Jeho jadro bolo vytvoren\u00e9 u\u017e v roku 1982. Z toho plyn\u00fa niektor\u00e9 nepr\u00edjemn\u00e9 d\u00f4sledky, na ktor\u00e9 sa vtedy nemyslelo.<\/p>\n<ul>\n<li>V\u0161etko, \u010do sa odosiela SMTP protokolom (vr\u00e1tane pr\u00edloh), mus\u00ed by\u0165 k\u00f3dovan\u00e9 v 7-bitovom ASCII k\u00f3dovan\u00ed. Z toho vypl\u00fdva, \u017ee aj text, aj bin\u00e1rne s\u00fabory v pr\u00edloh\u00e1ch musia by\u0165 prek\u00f3dovan\u00e9 do tohto k\u00f3dovania, \u010do \u201ezbyto\u010dne\u201c za\u0165a\u017euje procesor a zv\u00e4\u010d\u0161uje objem prenesen\u00fdch d\u00e1t. Roz\u0161\u00edrenie o prek\u00f3dovan\u00e9 bin\u00e1rne d\u00e1ta a d\u00e1ta v inom k\u00f3dovan\u00ed znakov umo\u017e\u0148uj\u00fa multimedi\u00e1lne roz\u0161\u00edrenia. Takzvan\u00e9 MIME (multimedia mail extension) typy v hlavi\u010dke mailu definuj\u00fa, ak\u00fdm k\u00f3dovan\u00edm boli tieto d\u00e1ta prek\u00f3dovan\u00e9 a ak\u00e9ho boli p\u00f4vodne typu.<\/li>\n<li>SMTP protokol nem\u00e1 \u017eiadnu autoriz\u00e1ciu. To znamen\u00e1, \u017ee m\u00f4\u017eeme posiela\u0165 maily z \u013eubovo\u013enej e-mailovej adresy. D\u00f4sledok je dobre zn\u00e1my. A\u017e\u00a0<a href=\"http:\/\/news.bbc.co.uk\/2\/hi\/technology\/7988579.stm\">97 %<\/a>\u00a0v\u0161etk\u00fdch e-mailov tvor\u00ed spam. Provideri \u010dasto robia (pseudo)opatrenie, \u017ee blokuj\u00fa odch\u00e1dzaj\u00facu komunik\u00e1ciu na port 25 a nedovolia tak svojim z\u00e1kazn\u00edkom prev\u00e1dzku SMTP serverov.<\/li>\n<\/ul>\n<p>SMTP spr\u00e1vy od servera s\u00fa jednoriadkov\u00e9 odpovede v tvare k\u00f3d a koment\u00e1r stavu. Klient zasiela bu\u010f pr\u00edkazy alebo obsah mailu pod\u013ea toho, v ktorej \u010dasti komunik\u00e1cie sa nach\u00e1dza. V pr\u00edpade, \u017ee je v stave, \u017ee pr\u00e1ve posiela mail, m\u00f4\u017ee zasiela\u0165 to\u013eko riadkov, ko\u013eko potrebuje. Koniec odosielania mailovej \u010dasti spr\u00e1vy oznamuje bodkou na samostatnom riadku. K jednotliv\u00fdm pr\u00edkazom sa nie je potrebn\u00e9 vyjadrova\u0165. Tie jednoduch\u00e9 s\u00fa samo vysvet\u013euj\u00face a zlo\u017eit\u00e9 si m\u00f4\u017eete pozrie\u0165 v\u00a0<a href=\"http:\/\/www.ietf.org\/rfc\/rfc2821.txt\">RFC 2821<\/a>. Odpor\u00fa\u010dam si pre\u0161tudova\u0165 zdrojov\u00e9 s\u00fabory va\u0161ich vlastn\u00fdch mailov. Uvediem iba jednoduch\u00fa komunik\u00e1ciu na odoslanie kr\u00e1tkeho mailu. \u201eC:\u201c ozna\u010duje riadok spr\u00e1vy klienta a \u201eS:\u201c riadok spr\u00e1vy servera.<\/p>\n<pre class=\"wp-block-preformatted\"><span style=\"color: #808080;\">S: 220 mail.ics.upjs.sk\r\nC: HELO doma.sk\r\nS: 250 Hello doma.sk, pleased to meet you\r\nC: MAIL FROM: &lt;alica@doma.sk&gt;\r\nS: 250 alica@doma.sk... Sender ok\r\nC: RCPT TO: &lt;bob@upjs.sk&gt;\r\nS: 250 bob@upjs.sk ... Recipient ok\r\nC: DATA\r\nS: 354 Enter mail, end with \".\" on a line by itself\r\nC: Prepacte, ze som pred tyzdnom neposlala projekt\r\nC: lebo som velmi chora\r\nC: .\r\nS: 250 Message accepted for delivery\r\nC: QUIT\r\nS: 221 mail.ics.upjs.sk closing connection\r\n<\/span><\/pre>\n<p>Je nutn\u00e9 poznamena\u0165, \u017ee mailov\u00fd server n\u00e1\u0161ho \u00fastavu, teda mail.ics.upjs.sk, je nastaven\u00fd tak, \u017ee nedovol\u00ed odosielanie mailov z in\u00fdch mailov\u00fdch adries ako registrovan\u00fdch. Nie v\u0161etky mailov\u00e9 servery toto dodr\u017eiavaj\u00fa.<\/p>\n<p>Ke\u010f mailov\u00fd server prijme od pou\u017e\u00edvate\u013ea mail, vlo\u017e\u00ed mail do radu mailov na odoslanie a n\u00e1sledne odosiela tento mail na cie\u013eov\u00fd server, dan\u00fd emailovou adresou prij\u00edmate\u013ea, op\u00e4\u0165 protokolom SMTP. Pokia\u013e je cie\u013eov\u00fd server do\u010dasne nedostupn\u00fd, pok\u00fa\u0161a sa o spojenie e\u0161te nieko\u013ekokr\u00e1t v priebehu najbli\u017e\u0161\u00edch hod\u00edn a dn\u00ed. Z\u00e1rove\u0148 upozor\u0148uje odosielate\u013ea o neschopnosti mail doru\u010di\u0165. Po doru\u010den\u00ed mailu na mailov\u00fd server prij\u00edmate\u013ea, je tento mail ulo\u017een\u00fd v jeho mailovej schr\u00e1nke a \u010dak\u00e1, kedy si ho pou\u017e\u00edvate\u013e vyzdvihne.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>SMTP: simple mail transfer protocol,\u00a0RFC 2821 SMTP protokol je ur\u010den\u00fd na odosielanie mailu od pou\u017e\u00edvate\u013ea k svojmu mailov\u00e9mu serveru a na odosielanie mailov od odosielate\u013eovho&hellip;<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[7],"tags":[],"_links":{"self":[{"href":"http:\/\/tech.sosthe.sk\/index.php\/wp-json\/wp\/v2\/posts\/289"}],"collection":[{"href":"http:\/\/tech.sosthe.sk\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/tech.sosthe.sk\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/tech.sosthe.sk\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/tech.sosthe.sk\/index.php\/wp-json\/wp\/v2\/comments?post=289"}],"version-history":[{"count":1,"href":"http:\/\/tech.sosthe.sk\/index.php\/wp-json\/wp\/v2\/posts\/289\/revisions"}],"predecessor-version":[{"id":290,"href":"http:\/\/tech.sosthe.sk\/index.php\/wp-json\/wp\/v2\/posts\/289\/revisions\/290"}],"wp:attachment":[{"href":"http:\/\/tech.sosthe.sk\/index.php\/wp-json\/wp\/v2\/media?parent=289"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/tech.sosthe.sk\/index.php\/wp-json\/wp\/v2\/categories?post=289"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/tech.sosthe.sk\/index.php\/wp-json\/wp\/v2\/tags?post=289"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}