Symptoms

After a change of the From Address for workflows, the workflows send emails but don't send notifications. Mail address was changed in the following locations: connection strings, string tables, K2 HostServer, K2 Setup Manager but notifications still doesn't work.
 

Diagnoses

Following things may be checked in this scenario:
When notifications are not being sent, are there any errors logged in Error Profiles? (K2 Workspace > Management > Workflow Server > Error Profiles > All)?

For K2 4.6.6 it is also necessary to adjust a section of the SourceCode.EventBus.Server.config, located in the following folder:
C:Program Files (x86)K2 blackpearlHost ServerBinSourceCode.EventBus.Server.config

Verify that you are not receiving only default notifications. Because Server Mail Events and InfoPath Client events there could be hardcoded From addresses instead of "From Address" field variable which is use for Default Client Events for example.
 

Resolution

Normally in such scenario it is sufficient to run K2 Setup Manager in configuration mode and after this also modify your workflow(s) to update the "From Address" with a new email address.