Mailing Slowing Down After About 30% Sent


New Member

I am seeing a major problem with the mailing. Initially it goes out fine sending about 500 emails per min to my MTA.

Then it starts slowing down, right now its at about 50% and only sending about 3 emails per minute to my MTA.

Why would this happen?
Which MTA are you using? How do you connect to it? Is it hosted on the same local network as MW?
Im using PMTA, connects via SMTP. It is not on the same network, but I have used this MTA setup to send over 500k emails without it ever slowing down... so its an issues with the mailwizz not mailing to the SMTP server
Hey Rob,

Yes the MTA receives and sends mail, until mailwizz stops sending...
I am going to check PHP memory, I just tried doing the parallel sending but I am getting a permission denied error when I run the command in SSH

chmod the parallel send script to 777 and then run the command with absolute path, so if you are on Ubuntu for example that would be:


Check what your current CPU/Memory & I/O usage is.
Ok, Script is running now... waiting to see if mail starts sending.

My system usage is very low under 25% so there is a lot of memory and processing available.
Still stuck:

Estimated completition rate 47.723% sent so far, that is 11,057 out of 23,169
Estimated completition duration 2 months, 3 weeks, 2 days, 6 hours, 39 minutes
The parallel daemon won't pick up that particular campaign as it has already been sent as far as MW is concerned. You may have hit a limit somewhere during this send and it won't budge further.

Do you have any messages in the MW application log? Delivery logs?
Ok, created a new campaign... started off great again. Sent to the MTA quick... and then within minutes fizzed out...
In the backend what do you have in your settings for Settings > Customer > Campaigns?
look at this post regarding cron settings as well. Personally I wouldn't disable some of the settings and allow a pause, it can be a couple of seconds.

I would also check to see how long it takes to open the SMTP connection.

If you are confident that you have tuned PHP correctly and MySQL and that you aren't hitting any limits with CPU/MEmory/Virtual Memory then you have to look at the connection to the SMTP server as many people are sending thousands of emails per hour with MW.

Some tips on MySQL (if run on separate server) tuning:

innodb_buffer_pool_size: Setting this to 70-80% of memory (server's RAM) is a safe bet. E.g. 12G on a server with 16GB of ram. You may want more if your running a dedicated server with mostly InnoDB.

*innodb_log_file_size: This depends on your recovery speed needs, but 256M seems to be a good balance between reasonable recovery time and good performance

*Note: If you modify innodb_log_file_size without removing the existing logs, MySQL will fail to restart and InnoDB will complain about the size of the changed log file.

This is the proper way to increase innodb_log_file_size:

- shutdown mysql server

- make backup of data and log files

- remove InnoDB log files

- set new value for innodb_log_file_size in my.cnf

- start mysqld

- check error logs to ensure everything went fine.

innodb_log_buffer_size: 4M is good for most cases

innodb_lock_wait_timeout: 300 (this is seconds) is good for most cases
Ok, I changed the values, added a 5 second pause.
I tested two campaigns, each about 10k subscribers. This time it sent a lot faster and more consistent but...

Both stopped sending right around 90%
Now, I have a bunch of ISPs blocked such as AOL and Comcast in the backend settings.
Would this be a reason its stopping at that number since its not sending to the full list?
I've never blocked any domains to be honest so I can't say if that's the case. If about 10% of your list is those domains then MW may calculate the % sent by how may emails were sent out minus the blocked ones if that makes sense?!!?

@twisted1919 is the best person to answer that one.

You could send a campaign to a list that hasn't got any blocked domains in it and see what happens.

But at least you are getting the speed up now.
Still not working....

So I added a larger list 50k and it stopped mailing again right around 10k.... something is getting stuck.
It sent nearly 10k to the SMTP server in about 10 min, but then it just stops.