import re
s="""(2021-07-29 01:00:00 AM BST)
---
peter.j.matthew has joined the conversation
(2021-07-29 01:00:00 AM BST)
---
john cheung has joined the conversation
(2021-07-29 01:11:19 AM BST)
---
allen.p.jonas
Hi, james
(2021-07-30 12:51:16 AM BST)
---
karren wenda
how're you ?
---
* * *"""
print(re.findall(r"^---[^\S\n]*\n(\S.*?)[^\S\r\n]*\n\S", s, re.M))
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