General questions about how to send mails in functions

[volkerSchule]

Hallo,

I have a larger project that should sent sometimes emails.
So my main Qt window has got several sub dialogs where I want to sent emails. Most of them contains functions that should sent several mails at once to different guys. So i want to run a loop in that functions for several (different) emails.

a) I don't know if I should do "auto server = new SimpleMail::Server;" only once in the main constructor of the program and use a global variable, or if i should do it in each constructor of every dialog or if i should do it in every function that sends mails.
b) I wonder if "auto server = new SimpleMail::Server;" needs a "delete server;" somewhere. Or if i better only use "SimpleMail::Server server" without "new".
c) Similar question as in a) just with "SimpleMail::ServerReply"

Thank you so much for your answer.

[dantti]

Server class is like QNetworkAccessManager you want only one in your application, unless you really want to send tons of emails at the same time, unlike QNAM each Server class represents a single connection to a server, so if you allocate 10 server classes that means 10 connections to your servers, so you likely want to keep one object around and just call send(mail) and they will be queued and processed in sequence.
if you don't dynamic allocate Server it will be deleted once the scope is done which in turn won't allow for the email to be sent at all, unless ofc you use QLocalEventLoop which is a bad habbit and might cause stack overflow and other issues....

[dantti]

Also it's not thread safe, so you need one Server class per thread.

[volkerSchule]

Depending on the user that use my software, I guess most of my users will sent around 100 to 2000 mails. (It is a software for schools. So larger schools have maybe around 2000 students. As far as I know the largest school in the world has got 40.000 students.)
hmmm... Not thread safe... I must think about that (I am sadly not very skilled). I am not sure how to delete a dynamic allocate Server if i do it per thread. I guess I will just try and check if Valgrind report me bugs if I do it wrong.

Just an other question: Is there a way how to stop sending the mails if there is an error? I mean: If i sent 100 mails and the first one answers with an error (I think i must display a QMessage to the user with the error report) it will be bad if he might get 100 error reports. So how can I stop sending the mails and stop reporting the errors?

[dantti]

You can either send one by one, and in case of an error you stop poping mails from your own queue.

You should likely just auto server = std::make_shared(); make sure not to pass this as parent then.

Since it's async you don't really need to worry about threads, unless you want a dedicated one or want to push
server's limits, it's usually fine to have lots of Server classes if you want to send more than one email per time, SMTP is not a fast protocol, the send/wait for reply makes it harder to be CPU consuming... reusing the same Server class means reusing the same TCP connection which is why it is important to keep the object alive (tho after a while the connection will drop)

[volkerSchule]

Thank you so much. I will try.

[volkerSchule]

Maybe my case is too special, but what do you think about adding features like:
.count() to check how many mails are still in the queue
.clear() to clear the queue
.setTimeDelay(int millis) to add a time delay before the next mail is send (Reason: I might need to sent more mails, but some mail provider have got limits like "max 500 mail per hour". So it would be nice to add an delay.