PHPMailer goes from 2.5.8 -> 2.5.9
Major changes according to their release post on GitHub (https://github.com/PHPMailer/PHPMailer/releases/tag/v5.2.9)

Major changes:
• The autoloader is no longer autoloaded automatically, and the PHPMailer class does not require the SMTP class explicitly, so you must either load the autoloader yourself (as all the docs and examples have done for the last year), or load the SMTP class yourself. This fixes the inability to substitute your own SMTP subclass, and also improves interoperability with other autoloaders.
• Support for data-uri images
• Debug output handling improved in SMTP
• You can now supply your own callable for debug output
• Avoid PCRE infinite recursion in some PCRE versions
• Consistency improvements
• Cleaned up example code See the changelog for more details.

PHPMailer/PHPMailer@v5.2.8...v5.2.9

Yaml goes from 2.5.5 -> 2.5.6. The changes for Yaml seem to be quite minimal
symfony/Yaml@v2.5.5...v2.5.6

Do these "major changes" create b/c issues for us?

This comment was created with the J!Tracker Application at issues.joomla.org/joomla-cms/4997.

We're loading via composer anyhow so the autoloading doesn't affect us. Everything else seems like bug fixes and features so I'm pretty sure no.

@test works

I could only test the mass mail function and that worked. Using the "Privat Messages Manager" and there selecting the recipients gives me a blank list although I have created a lot of users. I get the same result with a postgresql installation but in addition "::character varying" is display in the recipients field.

Users won't show there - only people with backend access and who can access the component

Thanks for the explanation. I didn´t use that component before. So, it works even with postgresql ;-).

@test:
Created a user from BE and received mail as new account has been created: OK
Created a user from FE and received mail as new account has been created: OK
Try to send an email link to friend: Not OK --> Email could not be sent (works OK before patch)
Private message to other super user: OK

@roland-d "Try to send an email link to friend" Where can I do that?

@waader It is the email option at any article (provided you have it enabled, which it is by default). See the screenshot for more details:

@wilsonge @waader The issue I found has nothing to do with this PR. The PR is sound and tested OK now.
The issue I see is related to this line:
https://github.com/joomla/joomla-cms/blob/staging/components/com_mailto/controller.php#L50
This gets triggered all the time, only if I hit the Send button quite regularly mails will go out but I can also get this warning quite regularly. It seems the spam protection is not so stable.

@roland-d Thanks for pointing me there. I can reproduce the issue.

Awesomes :) Can we merge this PR then and create an issue for com_mailto?

RTC anyhow with 2 good tests