To resolve the issue of new contacts not receiving SMS messages due to missing country codes in the mobile number field, the best solution is to select 'Normalize Phone Number' in Journey settings.
Normalize Phone Number: In Journey Builder's SMS activity settings, enabling the "Normalize Phone Number" option automatically formats phone numbers to the E.164 standard (e.g., +1 for US numbers) by appending the appropriate country code based on a specified default country (in this case, the United States). This ensures that phone numbers missing a country code are correctly formatted for SMS delivery.
Why it works:
SMS providers require phone numbers in E.164 format (e.g., +12025550123 for a US number).
If the mobile number in the Salesforce Entry Data Extension lacks the country code (e.g.,
2025550123), the SMS will fail to send.
Normalizing phone numbers at the journey level corrects this issue without requiring manual updates to Salesforce records.

A Query Activity can select subscribers who haven't purchased in six months based on date logic.
The results are saved into a Data Extension.
This Data Extension is then used as the entry source into a Journey, which can orchestrate sending across multiple channels (email, SMS, push).

Journey Builder is ideal for multi-step campaigns like sending a follow-up or reminder after the original message.
To send at the subscriber's optimized send time (OST), Journey Builder supports Einstein Send Time Optimization (STO).
A reminder email can be scheduled exactly 3 days after the initial send with dynamic optimization for each subscriber.

The Verification Activity is precisely designed for this two-part requirement: it evaluates the staging data extension against a defined row-count threshold (over 1,000 records) immediately after the Import activity runs, and if that threshold is breached, it can simultaneously send an email notification to the marketing manager and halt the automation before it proceeds to the subsequent SQL Query step. Placing it directly between the Import and SQL Query activities ensures that if the staging data is over-imported, the automation stops right there - preventing the downstream SQL Query from ever populating the sendable data extension that day, satisfying both stated requirements (notification and prevention of the sendable DE update) with a single, native activity requiring no custom development. Option C proposes writing a custom SSJS script to replicate this exact functionality manually, which is unnecessary and less maintainable than using the native, purpose-built Verification Activity that already provides both the conditional check and notification capability out of the box. Option B, splitting into two automations, does not itself provide the conditional row-count evaluation and stop logic - it ' s a structural change that doesn ' t solve the underlying validation requirement. Option D ' s Wait Activity pauses for time-based delay, not conditional record-count validation, and does not address the requirement at all. Reference: Automation Studio Verification Activity.