If the addresses  don't contain any spaces, I'd replace  SMTP with space SMTP and
.rib with .rib space, then use "text to columns" in the Data Menu to split up
the text into the bits you do and don't want. (If you have spaces you'll need to
find a character that doesn't appear in the strings of text.)You'll need to
insert a couple of columns to receive the split text, but they can be deleted
once you have the information you want.

I hope I'm not helping a spammer harvest email  addresses..
Assuming ".rib" comes directly at the end  of each email address:
If your string containing the email address  is in C30 then
=MID(C30,FIND("SMTP:",C30)+5,FIND(".rib",C30)-FIND("SMTP:",C30)-5)
should extract one email per line as long as '.rib' always comes after
'SMTP:'

Where I work we receive an Outlook address  book from another site to
import into ours for a consolidated address book. Unfortunately the
file we recieve has "junk" in with the email  addresses. Since it is
in .csv/excel format, I'm trying to help
sort it out for the folks to do the importing.. no spammer email
address harvesting issue here.

Anyway, when I tried your formula, I get an error #VALUE.. trying to
figure out why... but this looks like it might be promising.

The most likely reason for a #VALUE result is that either or both
'.rib' and 'SMTP:' are absent. Also happens if '.rib' comes before 'SMTP:'

Does '.rib' come immediately after each email  address?

For my test, I used the formula on this data  below, which is all run
together in one cell. I found my mistake, had .RIB in my formula in
caps, oops! However I have found that in some of my data .rib IS in
caps - .RIB, so I guess I'll need to get this uniform before I run the
Find function.

The FIND function did a nice job and returned the info in the middle  -
john.smith@... -which is great! But I still need the SMTP: at
the beginning and .rib at the end.

SMTP:john.smith@...%
400:c=US;a=DMS;o=OK2;s=Smith;g=John;i=W;ou1=HKNN1;%
MS:SILLMAIL/SILLPOX1/smithjb%CCMAIL:smith, john at SILL

you can use the wildcard find  and replace  facility in textpad or any other
text editor to do it .

copy the entire column to textpad ..

in the find what box type: (.*)(SMTP:.*.rib)(.*)
in the replace with box type: \2

check the regular expression checkbox and replace all..

I never knew that functionality was there - good stuff!
I couldn't do this in WordPad or NotePad but I could do it in Word. I
had a few difficulties with the dots but got this to work (after, as
John Marshall suggests, converting all upper case .RIB to .rib):

in the Find what box:
(*)(SMTP:*.rib)(*)

in the Replace with box:
\2^p

I've got it! Thanks Pascal! I just needed to adjust a couple of
numbers to get the SMTP and .rib to show up in the results! yeah!
Looks like this

=MID(L12,FIND("SMTP:",L12)+0,FIND(".rib",L12)-FIND("SMTP:",L12)--4)

I read a lot of messages but don't post too often. Pasxal
has it right most of the time. On this one, I just tweaked his
function a bit and came up with this:

=MID($A8,FIND("SMTP:",$A8),FIND(".rib",$A8)+4-FIND("SMTP:",$A8))


It seems to work, although I do see you have put in some constants
to get the job done.

You have most likely finished it all by now. I just had a suggestion for
the ".rib" and ".RIB" issue. By using an IF and ISERR statements, you
should be able to capture anyone of the two in the same formula.

=IF(ISERR(MID(L13,FIND("SMTP:",L13)+0,FIND(".rib",L13)-FIND("SMTP:",L13)
--4))=TRUE,MID(L13,FIND("SMTP:",L13)+0,FIND(".RIB",L13)-FIND("SMTP:",L13
)--4),MID(L13,FIND("SMTP:",L13)+0,FIND(".rib",L13)-FIND("SMTP:",L13)--4)
)

SMTP:john.smith@...
SMTP:john.smith@...

I'm coming in to this late in the game, but I would seriously consider
switching the string to upper case BEFORE processing.

To handle the possibility of .rib being .RIB, .Rib, .rIB etc. etc. you
can use the UPPER function thus:

=MID(A2,FIND("SMTP:",A2),FIND(".RIB",UPPER(A2))-FIND("SMTP:",A2)+4)

Until you recommended using UPPER, I was doing a find/replace
to change to all same case, but this function works like a CHARM!!

Thanks so much, I put the entire formula together in a Macro that does
a few other find/replace actions on other columns in the spreadsheet
and then attached the macro to a toolbar button to be used as
new "messy" files come in.