[Info-vax] bizarre SMTP problem

[Phillip Helbig---remove CLOTHES to reply]

In article <0026d30f$0$20626$c3e8da3 at news.astraweb.com>, JF Mezei
<jfmezei.spamnot at vaxination.ca> writes: 

> Phillip Helbig---remove CLOTHES to reply wrote:
> 
> > MAIL> send
> > To:     foo.bla+xxx at bar.doo.da
> > %MAIL-E-NOSUCHUSR, no such user FOO.BLA
> 
> 
> MAIL> send
> To:     system+jfmezei
> Subj:   test message
> Enter your message below. Press CTRL/Z when complete, or CTRL/C to quit:
> test
>  Exit
> New mail on node CHAIN from CHAIN::SYSTEM
> 
> And jfmezei got a copy as well.
> 
> aka: the + seems to be used as a "," to delimit multiple destinations

That's what I guessed.  Is this documented anywhere?