Describe configuration behaviour with multiple mailers

[xelan]

Q	A
Doc fix?	yes
New docs?	yes
Applies to	all
Fixed tickets	symfony/swiftmailer-bundle#111

This PR describes the behaviour when multiple mailers are configured.

[xabbuh]

I would reword this a bit:

.. caution::

    When configuring multiple mailers, options must be placed under the appropriate
    mailer key of the configuration. Options placed directly under the `swiftmailer`
    key will not be applied to all mailers, but will configure a mailer named
    ``default`` instead.

What do you think?

[xelan]

Thank you, Christian, I think your wording sounds great and explains the issue well.
If i interpret the configuration code correctly, the default mailer doesn't have to be named default, but it has to be configured as default_mailer.

Edit: Oh, seems like it simply uses the name default regardless of the configured default_mailer - This surprised me again 😄

I'll push a new commit to my PR which contains your rewording.

[xabbuh]

Thanks @xelan for making the documentation better! I have left just one minor suggestion. What do you think about it?

[xabbuh]

👍

[sstok]

👍

[xabbuh]

Hm, looking at the code again I think this only true if you do not change the default mailer using the default_mailer option (which defaults to default).

@stof What do you think?

[stof]

@xabbuh using the shorthand syntax in multiple files with a non-default name for the mailer indeed works only if you redefine the name in all files (the same is true for Doctrine shortcuts btw).
Anyway, the recommendation should be to never use the short syntax if you use multiple mailers (and to avoid changing the mailer name if you use only one, as you don't care about the name anyway in such case)

[arderyp]

Thanks @stof, @xelan, and everyone else for this info/work.

[wouterj]

Thanks @xelan for your contribution! I've merged your PR into the 2.3 branch. After the merge, I've changed the wording a bit in 34c0771 to not explain what happends if someone doesn't follow this recommendation (they should simply never do it).