@WarrenBelz
@Jagadeeshk
Hello,
A big thank you to the both of you for your advice! I really appreciate it. As you can see, the email formatting is really starting to take shape. Warren, I was able to get the email going with your suggestion to switch over to Office365Outlook.SendEmailV2. I do have a follow-up question for the both of you when it comes to displaying dollar signs in HTML. Here is what the email currently looks like. As you can see, the Total below the table displays as currency, but the figures within the table do not. I tried entering double quotes around the dollar sign and single quotes, but can't seem to get it right. Can you help me? If you scroll down, you'll see the revised table code. I've colored the Amount line red.
For the sake of reference the currency formulas in the app are:
Text property of the amount in the Collection is:
Text(Value(ThisItem.ExpenseAmount),"[$-en-US]$#,###.00")
Text property for the Total label in the app (the one outside the Collection) is:
"Total: " & Coalesce(Text(Sum(colExpenses,ExpenseAmount),"[$-en-US]$#,##0.00"),"$0.00")

Here is my revised HTML code. Jag, can you confirm I pared down the html code per what you had in mind?
Office365Outlook.SendEmailV2(varUser.Email,"418001 Admin Budget Expense Confirmation","
<html>
<head>
<style>
Table {
font-family:arial,sans-serif;
border-Bottom: 1px solid #ddd;
width: 50%;
border-collapse: collapse;
border-spacing: 5px;
}
td {
text-align: left;
padding: 8px;
border-bottom: 1px solid #ddd;
font-size: 12px;
border-collapse: collapse;
}
th {
text-align: left;
padding: 8px;
border-bottom: 1px solid #ddd;
font-size: 12px;
border-collapse: collapse;
}
</style>
</head>
<body>
<h3>Thank you for your report submission.</h3>
<p>Here is a summary of the expenses you entered into the budget tracking tool today. You can view or edit your submission at any time within the app: <a href='https://apps.powerapps.com/play/123?tenantId=123&hidenavbar=true'>418001 Admin Budget Tracking App</a>.</p>
<table>
<tr>
<th>Transaction Date</th>
<th>Budget Category</th>
<th>Sub-Category</th>
<th>Merchant</th>
<th>Amount</th>
<th>Description</th>
</tr>"
&
Concat(colExpenses, "<tr>
<td>" & TransDate & "</td>
<td>" & BudgetCategory & "</td>
<td>" & SubCategory & "</td>
<td>" & Title & "</td>
<td>'$' " & ExpenseAmount & "</td>
<td>" & Description & "</td></tr>") &
"</table></body></html><p>" & lblCollectionSum.Text, {IsHtml: true, Importance: "Normal"});