lib-smtp: client: Make clear that XCLIENT is not sent if the server has no support.

lib-smtp: client: Add support for connecting from an explicit source IP.

lib-smtp: client: Uncork and flush the output stream explicitly after sending commands. This allows detecting any output stream errors.

lib-smtp: client: Perform output stream error handling in one place.

lib-smtp: client: Flush and check output for errors after uncorking. Otherwise, a disconnection event may be missed.

lib-smtp: client: Handle output stream errors in a separate function.

lib-smtp: client: Use the new connection_input_halt/resume() functions.

lib-smtp: Recreate connection IO after streams change This fixes hangs after STARTTLS. Originally by Stephan Bosch

lib-smtp: client: Fix timeout leak sometimes occurring at unexpected remote disconnect. While disconnected, newly submitted commands are queued, yet scheduled for immediate failure. The timeout used for that was not cleaned up.

lib-smtp: client: Fix ignoring invalid certificate from server. Although it initially allowed the invalid certificate, it would still fail later on while reading/writing the SSL streams.

lib-smtp: client: Assign only connection settings during connection initialization. Due to some copy-paste mistake, some global client settings were assigned instead.

lib-smtp: client: Always use per-connection settings in connection. Some part of the connection code referred to global client settings.

lib-smtp: client: Properly allow per-connection SSL configuration. Although this was already partially possible, the connection was still always using the global client SSL context.

lib-smtp: client: Fix segfault occurring in connection when SSL certificate is invalid. The connection is using its own local SSL settings to determine whether an invalid certificate is allowed. However, these local settings were not properly initialized.

Updated copyright notices to include the year 2018.

lib-smtp: client: Fix rawlog input stream inconsistency by updating streams right after initializing TLS. Restructured the code to call a new function called smtp_client_connection_streams_changed() which performs all the necessary updates. Before, enabling rawlog could break the TLS handshake.

lib-smtp: client: Make smtp_client_connection_commands_abort() more reliable by copying the command lists. Copy the current lists of queued and waiting commands and reference each command before calling smtp_client_command_abort(). Aborting one command can cause other dependent commands to be aborted (in a transaction or from submission service), which could have caused trouble in this function.

lib-smtp: client: Make smtp_client_connection_commands_fail_reply() more reliable by copying the command lists. Copy the current lists of queued and waiting commands and reference each command before calling smtp_client_command_fail_reply(). Failing one command can cause other dependent commands to be aborted (in a transaction or from submission service), which could have caused trouble in this function. Problems would likely occur at connection disconnect.

lib-smtp: Implemented SMTP client.