sp_send_dbmail sends query results from one server but not a second server

Question

Both servers are able to normally send email without issue

server a is able to send the email for the query below, but server b has an error message saying, "mail could not be sent to the recipients because of the mail server failure. Exception message: Cannot send mails to mail server."

Test emails and other jobs with sp_send_dbmail steps work fine on both servers.

Doesn't matter if done as job or in a query window behavior on both servers is consistent.

Failing server is at 12.0.5203.0, working box is 12.0.5511.

Code is:

DECLARE @bodyMsg nvarchar(max)
DECLARE @subject nvarchar(max)
DECLARE @tableHTML nvarchar(max)
select cast(getdate() as date)
SET @subject = 'Detail' + cast(cast(getdate() as date) as varchar)

SET @tableHTML = 
N'<style type="text/css">
#box-table
{
font-family: "Lucida Sans Unicode", "Lucida Grande", Sans-Serif;
font-size: 12px;
text-align: center;
border-collapse: collapse;
border-top: 7px solid #9baff1;
border-bottom: 7px solid #9baff1;
}
#box-table th
{
font-size: 13px;
font-weight: normal;
background: #b9c9fe;
border-right: 2px solid #9baff1;
border-left: 2px solid #9baff1;
border-bottom: 2px solid #9baff1;
color: #039;
}
#box-table td
{
border-right: 1px solid #aabcfe;
border-left: 1px solid #aabcfe;
border-bottom: 1px solid #aabcfe;
color: #669;
}
tr:nth-child(odd) { background-color:#eee; }
tr:nth-child(even) { background-color:#fff; } 
</style>'+ 
N'<H3><font color="Red">Header</H3>' +
N'<table id="box-table" >' +
N'<tr><font color="Green">
<th>operation_id</th>
<th>event_message_id</th>
<th>Date</th>
<th>Time</th>
<th>Message</th>
<th>EventName</th>
<th>message_source_name</th>
</tr>' +
CAST ( ( 

SELECT 
td = operation_id,'',
td = event_message_id,'',
td = cast(message_time as date) ,'',
td = cast(message_time as time)  ,'',
td = MESSAGE ,'',
td = event_name ,'',
td = message_source_name
FROM   (
       SELECT  em.*
       FROM    SSISDB.catalog.event_messages em
       WHERE   em.operation_id = (SELECT max(execution_id) FROM SSISDB.catalog.executions where package_name='packagename.dtsx')
           AND event_name NOT LIKE '%Validate%'
       )q
ORDER BY message_time 
FOR XML PATH('tr'), TYPE 
) AS NVARCHAR(MAX) ) +
N'</table>' 

EXEC msdb.dbo.sp_send_dbmail @recipients='someone@somewhere.com',
@subject = @subject,
@body = @tableHTML,
@body_format = 'HTML' ;

Body is inline so CU4 isn't the issue. Any thoughts or suggestions would be appreciated.