Provided is a method and system for controlling access to a mail transfer agent (MTA), included in a mail server infrastructure (MSI), by a client, which is either a mail user agent (MUA) or an MTA not included in the MSI, and features determining whether to grant access to a client based upon the accesses made to this and other MTAs at the present time or in the past. To that end, the method includes receiving a request for access to the one of the plurality of mail transfer agents by the client. Access between the client and other MTAs is determined to obtain an existing access profile. A conditional access profile is developed from the existing access profile and from the request. The conditional access profile is compared against a permissible access profile to determine whether to grant the request. If it is determined that the conditional access profile does not violate the rules and criteria, the access is granted. Otherwise, access is denied. Also disclosed is a system that carries-out the functions of the method.