WooCommerce Shipping & Namecheap VPS Expert Needed

I am looking for an experienced WooCommerce & server (Namecheap VPS / Linux / cPanel) expert to help me fix multiple technical issues that appeared after migrating my website from shared hosting to a Namecheap VPS.
I need someone who understands WooCommerce internals, shipping logic, add-ons, and server email configuration.

WooCommerce Shipping Cost Issues (Add-ons)

Shipping rates disappear when certain add-on products are added to the cart

Add-ons are real products (not virtual)

Shipping works when:
Main product alone
Some add-ons only

Shipping fails when:
Specific add-on combinations
Add-on alone
Using Flexible Shipping
Product weights are set, but rules don’t always trigger
Need debugging + correct configuration (not workarounds)

2️⃣ Emails Not Being Received
Website shows “email sent successfully”
No emails arrive (order emails, test emails)
Issue started after VPS migration

Need to:
Check SMTP / ports
Server firewall
WordPress mail configuration
Ensure reliable email delivery

Recently migrated from shared hosting to Namecheap VPS
After migration:
Website sometimes slow
Cart & checkout behavior inconsistent
Email delivery stopped

VPS details:
Linux
cPanel
Need a full health check:
PHP / MySQL
Firewall
Email services
Performance issues


Experience with:
WooCommerce (shipping rules, add-ons, checkout)
Flexible Shipping plugin
Linux VPS (Namecheap preferred)
SMTP / mail debugging

Ability to:
Diagnose root causes
Fix issues properly (not temporary hacks)
Explain what was wrong and what was fixed