CRITICAL! Sent messages are getting into the spam folder of my clients!

CRITICAL! Sent messages are getting into the spam folder of my clients!

Hi,

I'm trying out Zoho Mail, I've configured everything in my webpage host, I'm able to send and receive messages. But I have these two problems:

1) The email I send from Zoho to my clients are arriving to their spam folder. This happens when I send emails using an alias from my account. This doesn't happen when I send them using the admin account, since I've added correctly the SPF record to my webpage host. Even so, THIS IS CRITICAL! I can't let that happen! It means that my clients are not receiving the important information I send to them. How can I solve this? This is a serious problem.

2) The email I send from my admin account arrives to the inbox of my clients, but 20 minutes delayed! I guess it shouldn't be that way, am I right?

Somebody help me please!
Thanks in advance.