Is SMTP based on TCP or UDP

Question

Is SMTP based on TCP or UDP   I really can t confirm it   In my opinion  SMTP should be based on UDP  but someone told me that is must be TCP

User · Answer

Seems the SMTP as internet standard uses only reliable Transport protocol  RFC821 has TCP  NCP  NITS as examples

User · Answer

In theory SMTP can be handled by either TCP  UDP  or some 3rd party protocol   As defined in RFC 821  RFC 2821  and RFC 5321      SMTP is independent of the particular transmission subsystem and      requires only a reliable ordered data stream channel    In addition  the Internet Assigned Numbers Authority has allocated port 25 for both TCP and UDP for use by SMTP   In practice however  most if not all organizations and applications only choose to implement the TCP protocol  For example  in Microsoft s port listing port 25 is only listed for TCP and not UDP     The big difference between TCP and UDP that makes TCP ideal here is that TCP checks to make sure that every packet is received and re-sends them if they are not whereas UDP will simply send packets and not check for receipt  This makes UDP ideal for things like streaming video where every single packet isn t as important as keeping a continuous flow of packets from the server to the client   Considering SMTP  it makes more sense to use TCP over UDP  SMTP is a mail transport protocol  and in mail every single packet is important  If you lose several packets in the middle of the message the recipient might not even receive the message and if they do they might be missing key information  This makes TCP more appropriate because it ensures that every packet is delivered

[tcp] Is SMTP based on TCP or UDP?

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