Well.

That this topic required so much of my attention is rather discouraging. The good news is I have an
answer despite the predictable lack of documentation on the topic. Hopefully, I am adding to the
body of knowledge for the benefit of others...

How do you tell Word to print Envelopes to the Envelope Feeder no matter which network printer a user
is currently connected to? If you've needed code to handle this you have no doubt discovered the
print job might produce a printer prompt asking you to manually feed the paper -- sometimes envelope,
sometimes letter size!!

I should now be confident that I have the Envelope Feeder bin designation situation under control.
[laugh track]
As Jefferson pointed out <!post=here,42652>here<!/post> and <!post=here, 57945>here<!/post>, I thought I bagged this bird
a while ago. But as reported in <post#=164653>post 164653</post#>, my confidence was shattered by the facts -- the
code just did not work consistently.

Even in the code gleaned and reworked from the above refs, this did not work:

Set oEnv = Dialogs(wdDialogToolsCreateEnvelope)
with oEnv
.AddrText = vEnvAddress
.EnvReturn = txtReturnAddress
.EnvOmitReturn = True 'No matter what, don't use the Word Return Address
If Me.optPrePrinted Then
If AutoTextExists(NormalTemplate, "EnvelopeExtra1") Then
AutoTextDelete ("EnvelopeExtra1")
End If
If AutoTextExists(NormalTemplate, "EnvelopeExtra2") Then
AutoTextDelete ("EnvelopeExtra2")
End If
Else
CreateReturnAddressBox (txtReturnAddress)
End If
.UseEnvFeeder = True
.PrintEnvLabel = True 'Thanks Jefferson
.Execute
End With
Set oEnv = Nothing

There's nothing here to tell Word the Envelope Size or the Envelope Bin.
.EnvPaperSize = 10 did nothing. The key is .EnvPaperName., but I had the
name wrong. The name to indicate is not the name in the printer properties,
(e.g. "Envelope Feeder", or "Automatically Select") but the name in the Envelope
Options dialog (Tools>Envelopes and Lables>Options>EnvelopeOptions>Envelope Size)
We use COM10 envelopes, so the name is "Size 10". If the Word Envelope Size does not match
the Windows printer properties size, Word will print the job to a manual feed bin!

So, here's the final product that seems to work no matter which printer I
change to (all our printers have an auto Envelope Feeder):

Set oEnv = Dialogs(wdDialogToolsCreateEnvelope)
with oEnv
.AddrText = vEnvAddress
.EnvReturn = txtReturnAddress
.EnvOmitReturn = True 'No matter what, don't use the Word Return Address
If Me.optPrePrinted Then
If AutoTextExists(NormalTemplate, "EnvelopeExtra1") Then
AutoTextDelete ("EnvelopeExtra1")
End If
If AutoTextExists(NormalTemplate, "EnvelopeExtra2") Then
AutoTextDelete ("EnvelopeExtra2")
End If
Else
CreateReturnAddressBox (txtReturnAddress)
End If
.UseEnvFeeder = True
.PrintEnvLabel = True 'Thanks Jefferson
.EnvPaperName = "Size 10"
.Execute
End With
Set oEnv = Nothing

One other line of code can help assure that the default
envelope size is set correctly for each document:

ActiveDocument.Envelope.DefaultSize = "Size 10"

This sets the

Tools>Envelopes and Lables>Options>EnvelopeOptions>Envelope Size

too and does not require an envelope added to the document.