SQL Server DB Mail will occasionaly use a crazy amount of memory and/or resources. I have added the following to SQL Servers for years as an Agent Job.

--Stop DBMail
use msdb;
go
execute dbo.sysmail_stop_sp;
go

--Start DBMail
use msdb;
go
execute dbo.sysmail_start_sp;
go

--Check the status of DBMail
use msdb;
go
execute sysmail_help_status_sp;
go