[exim] Quotes in address for callout

I am using exim-4.62.

I have just encountered a problem with callout, using it for sender
verification.

The address had an apostrophe in the local part, like

A.N.O'User@???

My logs indicate that the callout actually used

"A.N.O'User"@???

The quotes are not needed in this context, so were they put in by the callout
code or is it possible it was my configuration? The callout line in my ACL is
"accept verify = sender/callout=2m,maxwait=3m,connect=30s".

In the particular case I have the remote system rejects the address with quotes
but accepts it without them! The remote system evidently does not conform to
the RFC, but it would be nice not to have this complication.

Phil.
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Phil Chambers (postmaster@???)
University of Exeter