@Borys Peten I am not aware of the error but may be this might helpful https://www.wintips.org/fix-relay-access-denied-554-5-7-1-error-in-outlook/#:~:text=The%20%22Server%20Error%3A%20Relay%20Access,as%20a%20source%20of%20spam. and also make sure you turn on the Email capture plugin.