feat: add localName to smtp config

[sthh]

This PR introduces a new configuration courier.smtp.local_name that is passed to the SMTP dialer used in kratos courier.
The config value is used in the SMTP HELO/EHLO command and was previously hardcoded to localhost.
Some SMTP relays (e.g. Gmail) require a unique identifier during the HELO command and close the connection if a generic value like localhost is used. Therefore those SMTP relays can currently not be used with Kratos.

See https://support.google.com/a/answer/2956491?product_name=UnuFlow&hl=en&visit_id=637871815371283723-3216367043&rd=1&src=supportwidget0&hl=en

We recommend that you configure your mail server to present a unique identifier (such as your domain name or the name of your mail server) in the HELO or EHLO command in the SMTP relay connections your server makes to Google. Avoid using generic names such as "localhost" or "smtp-relay.gmail.com," which can occasionally result in issues with DoS limits.

Note that you may not be able to reproduce the bug with an Gmail SMTP relay, since Gmail does not close every connection. For us, it worked fine for some time before Gmail started to close the connections.

Related issue(s)

#2425

Checklist

• I have read the contributing guidelines.
• I have referenced an issue containing the design document if my change
  introduces a new feature.
• I am following the
  contributing code guidelines.
• I have read the security policy.
• I confirm that this pull request does not address a security
  vulnerability. If this pull request addresses a security. vulnerability, I
  confirm that I got green light (please contact
  [email protected]) from the maintainers to push
  the changes.
• I have added tests that prove my fix is effective or that my feature
  works.
• I have added or changed the documentation.

Further Comments

[codecov]

Codecov Report

Merging #2445 (ab19cac) into master (50bdba9) will decrease coverage by 0.04%.
The diff coverage is 100.00%.

❗ Current head ab19cac differs from pull request most recent head 4524927. Consider uploading reports for the commit 4524927 to get more accurate results

@@            Coverage Diff             @@
##           master    #2445      +/-   ##
==========================================
- Coverage   76.52%   76.47%   -0.05%     
==========================================
  Files         316      316              
  Lines       17596    17600       +4     
==========================================
- Hits        13465    13460       -5     
- Misses       3197     3205       +8     
- Partials      934      935       +1     

Impacted Files	Coverage Δ
courier/smtp.go	75.00% <100.00%> (+0.42%)	⬆️
driver/config/config.go	82.05% <100.00%> (+0.05%)	⬆️
cmd/courier/watch.go	64.40% <0.00%> (-11.87%)	⬇️
persistence/sql/persister_courier.go	86.76% <0.00%> (-2.95%)	⬇️

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[aeneasr]

Looking good! Could you please add this new key to the documentation? :)

https://www.ory.sh/docs/kratos/concepts/email-sms#sending-e-mails-via-smtp

[sthh]

Thank! I've added some docs in ory/docs#810

[vinckr]

Hello @sthh
Congrats on merging your first PR in Ory 🎉 !
Your contribution will soon be helping secure millions of identities around the globe 🌏.
As a small token of appreciation we send all our first time contributors a gift package to welcome them to the community.
Please drop me an email and I will forward you the form to claim your Ory swag!