Redmine

will reject the address, and thus the message.

This is related to your SMTP server.
But it's not a Redmine bug.

No, this isn't a mail server-specific issue. This is standard
for all mail servers
that process mail for a domain. If any recipient in the list
is invalid, the
message is rejected. This is why mailing list servers send messages
out one
at a time. This is why Trac sends them out one at a time. This
is why
Redmine should also be sending them out one at a time.

It's in RFC 821, section 3.1: "If the recipient is unknown
the receiver-SMTP
returns a 550 Failure reply."

This causes the message to fail in its entirety if there's a
bad recipient in the
address list and the server knows it.

Please send out messages one at a time. It's a simple loop. :)

If any recipient in the list is invalid, the message is

rejected.

I'm just trying to understand... If you're right, how do you
explain example 1 in RFC 821, page 5 ?

This is why Trac sends them out one at a time.

This was the case in 0.9, but not in 0.10.
I've just installed Trac 0.10.3 and I can guarantee that only
one notification is sent for all the recipients (bcc by default).
I think that rubyforge is also doing so.

I'm not saying it's invalid SMTP; it sends the messages more
often than not, so it
must be valid. I'm saying that in the specific case of company
foo.com running
redmine.foo.com and sending mail via mail.foo.com with users
a@foo.com through
z@foo.com that the mail server will be the final destination
for all of the messages.
As such, if someone accidentally uses the address AA@foo.com,
then the mail server
will reject the whole message because it knows that one address
is wrong and
absolutely no one that works with that user will ever get
a notification as a result.

This happens across mail server types, reliably. I've tested
two Postfix servers and
an Exim server on this and it fails every time if just one user's
email is incorrect AND
the server Redmine uses to send the message is the final destination
for that
message. It's not something one can easily fix.

Well, I could turn on soft failures on the server, but then when
the server is
spammed then it'll eat up a ton of resources and that's generally
not good. It would
be much nicer if Redmine had the option of simply firing them
off in a loop so that
one bad address doesn't break things.

+1

I can confirm this bug exists in version:

Environment:
  Redmine version                3.0.1.stable.14155
  Ruby version                   2.2.1-p85 (2015-02-26) [x86_64-linux]
  Rails version                  4.2.1
  Environment                    production
  Database adapter               Mysql2
SCM:
  Subversion                     1.8.8
  Git                            1.9.1
  Filesystem                     
Redmine plugins:
  agile_dwarf                    0.0.3
  clam                           0.0.1
  clipboard_image_paste          1.10
  redmine_image_clipboard_paste  1.0.0

Expected behavior would be to send emails to rest of users related to tasks (creator and watchers)

Dump from my production log, after updating an issue:

Started PATCH "/issues/185" for 8.8.8.8 at 2016-12-02 14:44:25 +0100
Processing by IssuesController#update as HTML
  Parameters: {"utf8"=>"✓", "authenticity_token"=>"MXd6g5H/bF8ZiF2TDabKInfV6Nh/N+pSzbIjo81LZfBl0OdxJ6FIkeA+UM6QmZB8CujKL5QiNiffWJIpaHKgEQ==", "issue"=>{"is_private"=>" 
0", "project_id"=>"20", "tracker_id"=>"5", "subject"=>"Something", "description"=>"Some desc.", "status_id"=>"3", "priority_id"=>"2", "assigned_to_id"=>"5", "fixed_version_id"=
>"", "parent_issue_id"=>"", "start_date"=>"2016-12-02", "due_date"=>"", "estimated_hours"=>"", "done_ratio"=>"100", "notes"=>"", "private_notes"=>"0", "lock_version"=>
"4"}, "time_entry"=>{"hours"=>"", "activity_id"=>"", "comments"=>""}, "last_journal_id"=>"116", "commit"=>"Submit", "id"=>"185"}
  Current user: aco (id=3)
  Rendered mailer/_issue.text.erb (4.8ms)
  Rendered mailer/issue_edit.text.erb within layouts/mailer (5.5ms)
  Rendered mailer/_issue.html.erb (2.7ms)
  Rendered mailer/issue_edit.html.erb within layouts/mailer (3.4ms)
Email delivery error: 550 5.1.1 <elliott@someserver.biz>: Recipient address rejected: User unknown in virtual alias table

This issue has persisted for years, and is now in the current version, 3.4.6.

It has affected us here at the Senate on multiple occasions when an employee leaves the Senate. That employee's email address is disabled, so any mail sent to that address returns a 550 SMTP error.

This has the end result of preventing ANY notifications from going out on a project where the terminated employee might be a member. This is bad behavior, and it's been reported multiple times.

I am asking that this issue be prioritized. We depend on email notifications working properly, and we don't want project notifications to stop working just because one member on that project/group has a bad email address.

This problem was fixed by #26791 in Redmine 4.0.0.