I think it is more than 30 slots. 50 is the number I remember, and I have gone over 30 quite a few times.
I do know like on the PTS where they use the Rewards of the Worthy system to distribute armor, the emails keep showing up as I delete them. And, these are way more than 30 emails in the que. But I have not had enough sales to worry about filling up my inbox. And I am not polling my characters running hirelings nearly as often as I used to.
So, long story short, I think you will get your mails, but not sure.
Oh, make sure you edit your Roster Note to say you will out of town for a couple of weeks, so the Inactive Policies, if there are any, take effect on you. Maybe ping the GM too and let them know. Social Guilds are less strenuous about this than Trading Guilds are.