set nocount on
create table #myTable (emailfrom varchar(50), emailto varchar(50))
go

insert #myTable 
select '<salesperson4@ mydomain.com>',  'emailcontact234@somedomain.com' union all
select '<salesperson4@mydomain.com>', 'emailcontact989@somedomain.com' union all
select '<salesperson8@mydomain.com>', 'emailcontact111@somedomain.com' union all
select '<salesperson8@mydomain.com>', 'emailcontact555@somedomain.com' union all
select '<salesperson2@mydomain.com>', 'emailcontact33@somedomain.com' union all
select '<salesperson5@mydomain.com>', 'emailcontact888@somedomain.com'  union all
select '<salesperson2@mydomain.com>', 'emailcontact890@somedomain.com'  union all
select '<salesperson1@mydomain.com>', 'emailcontact890@somedomain.com'  union all
select '<salesperson1@mydomain.com>', 'emailcontact777@somedomain.com' union all
select '<salesperson1@mydomain.com>', 'emailcontact22@somedomain.com'  union all
select '<salesperson1@mydomain.com>', 'emailcontact1@somedomain.com'


print '--all emailTo values that have been contacted my multiple salespersons'
select  emailTo
from    #myTable
group by emailTo
having count(distinct emailFrom) > 1


print '--the sales people that contacted those emails'
select	*
from	#myTable
where	emailto in 
	(
	select  emailTo
	from    #myTable
	group by emailTo
	having count(distinct emailFrom) > 1
	)

go

drop table #myTable

output:

--all emailTo values that have been contacted my multiple salespersons
emailTo                                            
-------------------------------------------------- 
emailcontact890@somedomain.com

--the sales people that contacted those emails
emailfrom                                          emailto                                            
-------------------------------------------------- -------------------------------------------------- 
<salesperson2@mydomain.com>                        emailcontact890@somedomain.com
<salesperson1@mydomain.com>                        emailcontact890@somedomain.com