Validating E-mails using message posting services

A computer system for validating e-mails, the computer system comprising:

• one or more computer processors;
• one or more computer readable storage devices;
• program instructions stored on the one or more computer readable storage devices for execution by at least one of the one or more processors, the program instructions comprising:
• program instructions to receive an e-mail;
• program instructions to determine a sender of the e-mail;
• program instructions to identify an account of a message posting service, wherein the account is associated with the sender;
• program instructions to query a message posting service for a first hash value corresponding to the e-mail based, at least in part, on the account;
• program instructions to, responsive to determining that the first hash value is posted to the account, calculate a second hash value based, at least in part, on one or more predetermined portions of the e-mail and to compare the first hash value and the second hash value;
• program instructions to, responsive to determining that the first hash value is equal to the second hash value, determine that the e-mail is authentic based, at least in part, on the comparison of the first and second hash values;
• program instructions to, responsive to determining that the first hash value is not equal to the second hash value, determine that the e-mail has been tampered with;
• program instructions to determine a time of receipt of the e-mail;
• program instructions to determine a time of posting of the first hash value;
• program instructions to determine a duration of time between the time of receipt and the time of posting;
• program instructions to, responsive to determining that the first hash value is equal to the second hash value and that the duration of time between the time of receipt and the time of posting is less than a threshold duration of time, determine that the e-mail is authentic;
• and
• program instructions to, responsive to determining the that the duration of time between the time of receipt and the time of posting is equal to or greater than the duration of time, determine that the e-mail has been tampered with.